Popular Science Monthly/Volume 22/January 1883/Scientific Farming at Rothamsted II
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Scientific Farming at Rothamsted II
By Manly Miles
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By MANLY MILES, M.D.
THE primary and leading object of the experiments with animals, which have been conducted at Rothamsted during the past thirty-five years, was the solution of practical agricultural problems; but, as in the case of the field experiments already noticed, the practical lines of inquiry have naturally led to the investigation of a wide range of topics belonging to the science of biology, which, in themselves, are of more particular interest to the physiologist, or even to the student of sanitary or of social science, than to the farmer.
From the number of animals under experiment, and the well-planned and thorough methods of investigation, in all departments of the experimental work, the results obtained have been of great value, not only from the light thrown on many of the obscure processes of nutrition, but also in laying a foundation for a consistent system of feeding, in which the relations of the food consumed to the special animal products obtained, and to the value of the manure produced, as an incident of the process, are clearly traced.
In determining the amount of food and of its several constituents consumed for a given live weight of the animal in a given time, aud the amount of food and of its several constituents required to produce a given amount of increase in live weight, several hundred animals, including oxen, sheep, and pigs, were subjected to experiment. In these researches, selected lots of animals were supplied, for weeks or months, with weighed quantities of food of known composition, as de- termined by analysis, and especially adapted to the particular point under investigation. The animals were weighed at the beginning, at intervals during the progress, and at the close of the experiment.
The composition of the manure produced from a given amount and quality of food consumed, by oxen, sheep, and pigs, was determined in a large number of cases by analyzing average samples of the food, and then making an analysis of the solid and liquid excretions of the animals. In these experiments, the oxen were fed in boxes in which the manure was preserved with litter of known composition. After feeding for from five to nine weeks, the total manure produced was carefully mixed, weighed, sampled, and analyzed. By this method the solid and the liquid exci-eta were not separately examined. With sheep no litter was used, the animals, in lots of five, being fed on a slatted platform with an inclined floor of sheet-zinc below it, so that the urine was drained into carboys containing acid, while the solid excretions were separately removed several times a day and preserved for analysis. The constituents determined in the food and in the ma- nure in the experiments with oxen and sheep were dry matter, mineral constituents, and nitrogen, and in some cases woody fiber. As an illustration of some of the difficulties that must be overcome in mak- ing exact investigations of this kind, a more particular description of some of the devices resorted to will be of interest. "In the case of pigs, individual male animals were experimented upon, each for pe- riods of three, five, or ten days only. Each animal was kept in a frame, which prevented it from turning around, and having a zinc bottom, with an outlet for the liquid to run into a bottle, and it was watched night and day, and the voidings carefully collected as soon as passed, which could easily be done, as the animal never passed either fseces or urine without getting up, and in getting up he rang a bell and so attracted the notice of the attendant. The constituents de- termined were, in the food and fseces, dry matter, ash, and nitrogen, and in the urine, dry matter, ash, nitrogen, and urea."
The amount and relative proportion of the different organs and parts of the body were determined in two hundred and forty-nine sheep, fifty-nine pigs, two calves, two heifers, and fourteen bullocks. As the object of this investigation was to obtain average data as to the proportions of the valuable carcass parts and the less valuable offal parts, in animals in different conditions as to fatness, a variety of animals were examined. The sheep under experiment may be grouped as follows: five sheep of different breeds in the lean or store con- dition; one hundred sheep of different breeds moderately fattened; forty-five sheep of different breeds excessively fattened; seventy- eight Hants Down sheep moderately fattened on different foods; and twenty-one sheep of different breeds and modes of feeding of more than average fatness. The fifty-nine pigs were moderately fattened on a variety of fattening foods.
The percentage weights of the different parts of the body of the three classes of animals, and of the sheep in the store, the fat, and the very fat condition, are given in the following condensed table from Dr. Lawes's lecture before the Royal Dublin Society:
PARTS OF THE BODY.
of 16 oxen.
of 249 sheep.
of 5 store 6heep.
Average of 45
very fat sheep.
7-0 3 8
Internal loose fat
Heart, aorta, lung3, windpipe, liver ) and gall-bladder, with contents, > spleen, pancreas, and blood. .....)
Other offal parts
Total offal parts
Loss by evaporation, etc
It will be seen that the stomach and contents make up 11*6 per cent of the live weight of the oxen, 7*5 per cent of the live weight of the sheep, and but 1*3 per cent of the live weight of the pigs, while the intestines and contents rank in the inverse order, giving- the high- est percentage in pigs and the least with the oxen. If the stomachs and intestines are taken together, we find the highest percentage in the oxen and the least percentage in the pigs. These figures corre- spond very closely to the relative amount of work required in the digestion of the food of the different animals, which is coarse and more bulky in the case of the oxen, and comparatively concentrated and of higher nutritive value in the case of the pigs. The greater relative development of the intestines in pigs has a probable relation to the more complete assimilation of the food of these animals. As a whole, the glandular and circulatory organs, which are grouped together in the table, are nearly in the same proportion in the three groups of vol. xxii. 25 animals, the range of variation being but little more than one half of one per cent. It should be stated that the much smaller percentage of offal parts, and the corresponding larger percentage of carcass, in the pigs, is partly to be attributed to the head and legs being included with the carcass of the pigs, while they are reckoned as offal parts in oxen and sheep. With sheep there was a rapid decrease in the per- centage of offal parts as the animals fattened, while the percentage of carcass increased from 53*4 in the store condition to 64*1 in the very fat condition. There was, however, an actual increase in the offal parts from the store to the very fat condition in the proportion of one to one and three quarters, but the carcass parts made a greater actual increase, one pound in the store condition being raised to two and one half pounds in the very fat condition.
In connection with the data furnished by the mass of facts relating to the relative proportion of organs and parts of the body, which we can not discuss in detail, it became a matter of interest to ascertain the chemical composition of the increase of fattening animals obtained from different articles of food, so that the relations of the food con- stituents to the constituents of the increase coidd be determined. As a chemical analysis of a living animal can not be made, it is of course impossible to determine directly the chemical composition of the in- crease, as an analysis would be required at the beginning and at the close of the fattening period. The composition of the increase of fattening animals must therefore be determined by indirect methods, as by calculation from the data furnished by the differences in the composition of the food and the excretions; or from assumed con- stants, in the form of averages obtained by analyzing a large number of representative animals.
The most satisfactory data relating to this subject, that have ever been published, will be found in the results of the numerous analyses of the entire bodies and parts of animals, in different conditions a3 to fatness, that have been conducted at Rothamsted. Determinations were made of the fat, nitrogenous substance, and mineral matter of the entire body, and of certain separated parts, of ten animals, de- scribed as follows: 1. A fat calf, of the shorthorn breed, nine or ten weeks old, taken from its dam, feeding on grass; 2. A half-fat Aber- deenshire ox, about four years old, fed on fattening food, but which had grown rather than fattened; 3. A moderately fat Aberdeenshire ox, about four years old; 4. A fat Hampshire Down lamb, about six months old; 5. A Hampshire Down store sheep, about one year old;
6. A half-fat Hampshire Down ewe, three and one fourth years old;
7. A fat Hampshire Down sheep, one and a fourth year old; 8. A very fat Hampshire Down sheep, one and three fourths year old; 9. A store pig; 10. A fat pig. The pigs were of the same litter, and, when selected, were as nearly as possible alike, one weighing one hun- dred pounds and the other one hundred and three pounds. " One was slaughtered at once, and its contents of nitrogenous substance, fat, mineral matter, etc., accurately determined. The other was fed on a mixture consisting of bean-meal, lentil-meal, and bran, each one part, and barley-meal three parts, given ad libitum, but accurately weighed, for a period of ten weeks, when it had nearly doubled its weight. The animal was then slaughtered, and analyzed as the other had been. The composition of the food was also determined by analysis."
According to the generally accepted theory of nutrition at the time the Rothamsted feeding experiments were planned, the constituents of foods were divided into two leading groups, each of which was assumed to serve a special purpose in the system. It was believed that the nitrogenous constituents were the only nutritive elements, and that the carbonaceous constituents (including the fat, starch, etc.) served as fuel, which was burned in the system to keep up the animal heat. In the published analyses of animals and of foods at Rotham- sted, this distinction was recognized, and the results are given in terms of these groups of constituents. A summary of the results of the analyses of the ten animals described above is given in the following table, in percentage values of groups of constituents, in the carcass and in the total offal parts:
Mineral mattor <ash).
a > 1
Half- fat old sheep . ...
This table furnishes some important data for an intelligible discus- sion of the economics of nutrition, with reference to human dietaries, but there are many points of interest presented in the details of the analyses of these animals that can not be embraced in such a tabular abstract. In the carcass of the fat calf, it will be noticed, the per- centage of nitrogenous substance and of /at is the same, while in the other animals the fat is largely in excess, even in those in store con- dition. There is likewise a larger percentage of nitrogenous substance in the offal parts than in the carcass in all cases. It was also found that < the fat of the bones bears but a small proportion to that of the whole carcass, while, of the whole of the nitrogen of the carcasses, perhaps not less than one fifth will be in the bones. . . . As the animal matures, the mineral, the nitrogenous, and the fatty matters all in- crease in actual amount; but the percentage of both mineral matter and nitrogenous substance decreases, while that of the fat increases so as to much more than compensate for the decrease in that of the other solid matters. The result is that there is an increase in the percentage of total dry substance." The young animals, as the lamb and calf, had a larger proportion of water in the carcass than other animals in the same condition; and there was a larger proportion of bones in the carcass of the calf than in the carcass of the other animals.
In estimating the composition of the increase in live weight of fat- tening animals it was assumed that the composition of the original weight, that is, the weight at the beginning of the feeding period, was the same as in the "store" or "half- fat" animals that had been analyzed; and that the composition of the animal at the close of the feeding period was the same as that of the "fat" or the "very fat" animal that had been analyzed. By a proper exercise of judgment as to the comparative condition and quality of the animals at the begin- ning and end of the feeding period, and applying the data derived from the analysis of animals of similar quality, a close approximation to the composition of the increase could thus be obtained, and the probable error would be reduced to a minimum when the averages were made up from a large number of animals. In this way the com- position of the increase was estimated in the case of ninety-eight fat- tening oxen, three hundred and forty-nine fattening sheep, and eighty fattening pigs, divided into numerous classes according to breed, con- dition of maturity, and description of food consumed. The estimated average percentage of mineral matters, nitrogenous substance, fat, and total dry substance, in the increase of these animals, is given in the following table:
Mineral matter (ash).
98 oxen average
1-47 2-34 0-06 0-53
TG9 7-13 644 7"76
66-2 70-4 71-5 631
349 sheep "
80 pigs "
The averages of all the animals under experiment, fed under a variety of conditions, and including the "fat" and the "very fat," are here given. In the tables which follow, however, data from selected cases are made use of, which do not change the general results, but represent, it is believed, more nearly, the results obtained in ordinary farm practice.
The percentage of mineral constituents in the increase of the sheep as given in the table is undoubtedly too high, from the presence of foreign matters in the wool which could not well be separated; this will of course affect the percentage of total dry substance which is the sum of the figures given in the three preceding columns.
We may now consider the relations of the constituents of the food to the constituents stored up in the increase. In the experiments to determine the amount of food and of its several constituents, con- sumed by an animal of given weight within a given time, and required to produce a given increase in live weight, the foods presented a wide range of variation in composition, and the rations were so planned that the animals had a supply of ad libitum food containing more or less nitrogenous substance, that enabled them practically to fix for themselves the relative proportions of the nitrogenous and non-nitroge- nous constituents consumed. In all of the feeding experiments it was found that the amount of food consumed by a given live weight of the animal, within a given tine, and also the increase in live weight obtained from it, depended more upon the non-nitrogenous constitu- ents, or even on the total dry substance, than upon the nitrogenous constituents, which had been generally assumed to be the true measure of nutritive value. In experiments with animals expending their energies in the form of work, the same demand for the non-nitrogenous constituents of the food was observed as in the case of fattening ani- mals. A certain moderate amount of nitrogenous substances was evidently needed in the food, but any increase beyond this required quantity had no influence upon the returns obtained for food con- sumed, either in the form of muscular force in working animals, or in increase in live weight in those that were fattened, or even on the amount of nitrogen contained in such increase. The nitrogen dis- charged in the urine, in the form of urea, was found to have no rela- tion to the activity of the muscles, but it was directly increased by an increment of nitrogenous materials in the food. The age and habits of the animals themselves, when growing or fattening, seemed, how- ever, to determine, to some extent, the proportions of nitrogenous materials in the stored-up increase.
The average results show that oxen supplied liberally with food of good quality, containing a moderate proportion of grain or other con- centrated food, would consume at the rate of from twelve to thirteen pounds of dry substance * per week for each hundred pounds of their weight, and that one pound of increase in live weight would be re- turned for it. Sheep, of several different breeds, consumed, on the average, about fifteen or sixteen pounds of dry substance of slightly better food per week for each hundred pounds of live weight, and re- turned about one pound of increase in weight for each nine pounds of dry substance in their food. Pigs, with food composed largely of
- Cattle-foods differ widely in the amount of contained water; the average being in
hay from ten to fifteen per cent, in grain from eight to fifteen per cent, and in roots from seventy-five to ninety per cent. The strictly "dry substance," excluding this variable element of water contents, is therefore taken as a basis in estimating nutritive values. grain, consumed from twenty-six to thirty pounds of dry substance per week, for each hundred pounds of live weight, and yielded one pound of increase in weight for each four or five pounds of dry sub- stance in their food. Oxen, therefore, consume more dry substance of food, in proportion to their weight, than sheep, and sheep consume more than pigs, while, in return for feed consumed, pigs yield more than sheep, and sheep gave better results than oxen. It must be re- membered in this connection, as has already been pointed out, that the food of oxen contained more woody fiber, while that of the pigs was comparatively concentrated and digestible, and therefore of better quality. With sheep of different breeds it was found that, under the same conditions as to age and fatness, the food consumed was in pro- portion to their live weight. The relative value of the larger and smaller breeds seems, therefore, to depend, to a great extent at least, upon their habits and hardiness, and their adaptation to the conditions of the locality in which they are placed.
In studying these experiments, it will be well to keep in mind the twofold function of food in the animal economy: first, as the source of energy for the performance of work in the various organs of the body, which is required in elaborating the peculiar animal products sought in the process of feeding (as milk, flesh, wool, etc.), and in car- rying on the processes of repair and reconstruction to maintain the in- tegrity of the animal machinery; and, in the second place, as supplying the materials for the construction or elaboration of the special animal products. The popular notions of nutrition assume that this supply of materials in the food for the new product sought is the most impor- tant, and the supply of energy for the performance of work is over- looked or assigned a subordinate position.
The results of the experiments relating to the use and ultimate dis- position of the food consumed by animals when fattened under average conditions, as to feed and increase, are given in the following table:
Each 100 pounds of dry substance in the food consumed was disposed ofcs follows:
Stored up as increase.
Used in internal work of the system, and not accounted for in manure or increaso.
36-5 319 16-Y
The figures in the last column of the table are not intended to rep- resent all of the internal work of the system. They simply show the amount of non-nitrogenous constituents that are not accounted for in the stored-up increase, or in the manure, and thus are properly desig- nated as having been used in internal work. From an agricultural etand-point, the proportions of food-constituents stored up as increase, and voided as manure, are of the first importance, as these are the two factors that determine the economy of feeding. The expenditure of energy in the system, from the nitrogenous constituents of the food, is not, therefore, included in the last column, as all of the nitrogen of the food that is not stored up as increase is finally excreted in the urine. The first and second columns of the table, therefore, include the ni- trogenous and the mineral substances of the food, and any energy that may have been expended as a result of their metamorphoses is not represented in the table.
From the data presented, it appears that more than one half (57*3 per cent) of the food of oxen when fattening is required in internal work, or in keeping the animal machinery in repair, to say nothing of the energy expended by the nitrogenous constituents, while but 6 - 2 per cent is stored up as increase in weight, and more than one third is found in the manure. With sheep, 8*0 per cent of the food is stored up as increase, less than one third appears in the manure, and 60*1 per cent is used in work of the system. The pigs give 17*6 per cent of the food in increase, or more than twice as much as the sheep, while nearly two thirds is required for internal work, and the manure con- tains less than one half as much as in the case of the oxen. The pigs store up a much larger proportion of their food as increase than either the sheep or the oxen, but a larger percentage is used in internal work, and less appears in the manui*e. The increased expenditure in work would naturally follow from the larger amount stored up as increase, which involves as a matter of course an expenditure of energy in its elaboration. But this is not the whole truth, as will be seen on mak- ing a comparison of the figures in the first and last columns of the table. For a given amount of increase stored up, the oxen actually expend more in internal work than sheep, and the sheep expend more than the pigs It evidently costs more, in internal work of the sys- tem, to elaborate the stored-up increase from the crude feed of the oxen than from the more nutritive food of the pigs. When the facts are examined from a different stand-point, the relations of the increase to work of the system will be more clearly seen, as in the following table, which gives the results obtained from a given live weight of the animals in a given time:
For each 100 pounds of live weight, per week.
Stored as increase.
Consumed in food.
Recovered in manure.
Used in internal
work of the
system, and not
in manure and
Used in internal work for each one pound of
Pounds. 1-13 176 6-43
Pounds. 12-5 160
Pounds. 4-56 5.10 4-51
Pounds. 7-16 962
Pounds. 6-34 5-47 2-76
Pigs The oxen make in increase but little more than one per cent of their weight per week, the sheep make one and three fourths per cent, and the pigs nearly six and one half per cent of their weight per week. Nearly the same amount of dry substance of the food appears in the manure of the different animals per week for each hundred pounds of their live weight. In proportion to their weight, the pigs consume more food, and a larger amount of food-constituents is actually used in work of the system, but, from the greater rate of increase, the work required to produce a pound of increase is less than one half of that required in oxen. These facts are of particular interest in connection with the differences already noticed (page 384), in the relative percent- age weights of the digestive organs of oxen, sheep, and pigs.
The dry substance of the food has alone been taken into the account in the preceding table, but, if we trace the final disposition of its sev- eral constituents in the system, we shall find marked differences in the proportions of each that are stored up as increase, voided in manure, or used in work of the system. The percentage of each group of food- constituents stored up as increase and voided in the manure is given in the next table:
CONSTITUENTS OF FOOD
Each 100 pounds of food-constituents consumed was disposed of as follows:
Stored up in increase.
Voided in mature.
Non-nitrogenous substance. . . . Mineral matters
Sheep. 4-2 94 31
Oxen. 95-9 14-1 98-0
The nitrogenous substance and mineral matters, as will be seen, are all accounted for in the stored-up increase and the manure, but there remains from 77'4 to 81*7 per cent of the non-nitrogenous substances that can not be found in the increase of the body or in the residual manurial excretions, as they have been used in internal work and ex- creted in the process of respiration.
Sheep store up as increase a larger proportion of all the food-con- stituents than oxen, and pigs store up a much larger proportion than sheep. The percentage of nitrogenous constituents stored up as in- crease or voided as manure will vary widely with different foods. We have seen, as a result of these experiments, that but a small proportion of nitrogenous substance was required in the food, and that the needed amount was comparatively constant under varying conditions. If the food contains but a moderate amount of nitrogenous substance, a larger percentage of it will be required by the system, and the amount ap- pearing in the manure will be so much diminished; but with highly nitrogenous foods a small percentage of the nitrogenous constituents will suffice for the purposes of the system, and the excess will appear in the manure. Among the many important results obtained in the experiments at Rothamsted, the data furnished for estimating the relative value of barn-yard manures are of particular interest. The essential constitu- ents of barn-yard manure, or those having a commercial value, are nitrogen, potash, and phosphoric acid, which are of course derived from the feed consumed by the animals making the manure. The composition of the food being known, the percentage of its several constituents that are voided in the manure may be estimated from the data obtained in these experiments, so that the relative value of the manure produced from different articles of food can be determined with sufficient accuracy for all practical purposes. From the results of the Rothamsted feeding experiments, we can not avoid the conclusion that the cereal grains and the highly nitrogenous linseed and cotton- seed cakes have essentially the same value as fattening foods, and that there is but little, if any, difference in the feeding value of timothy and clover hay. When the production of manure is concerned, how- ever, the clover has a much higher value than timothy, and the linseed and cotton-seed cakes are worth very much more than the cereal grains. That is to say, the digestible and available non-nitrogenous constitu- ents of the food determine its nutritive value, provided always the moderate required supply of nitrogenous materials is present, and the comparative manurial value is determined by the nitrogenous constitu- ents. A variety in the ration would undoubtedly be desirable for nutritive purposes, as the best results can not be obtained with any single article of diet.
From the facts already presented it appears that a large proportion of the increase of fattening animals, in many cases more than two thirds, is fat. It was formerly supposed that the fat of animals was derived from the fatty materials in the food, but this source was found to be entirely inadequate. The non-nitrogenous constituents of the food the carbo-hydrates were then quite naturally looked upon as the source from which the fat was elaborated; but afterward Pro- fessors Voit and Pettenkofer insisted that the fat of animals was almost exclusively formed from the nitrogenous constituents of the food. In experiments with pigs, which are evidently the most suitable animals for experiments relating to the formation of fat, Drs. Lawes and Gil- bert conclusively show that, with foods in which the ratio of the ni- trogenous to the non-nitrogenous constituents was a suitable one for fattening purposes as in Indian corn and barley a large proportion of the fat in the stored-up increase must have been produced at the expense of the non - nitrogenous constituents. There was also evi- dence that the nitrogenous constituents of the food, when in excess, might replace the carbo-hydrates, to some extent, in the formation of fat.
The analysis of the entire bodies and parts of the ten animals made at Rothamsted furnish some interesting data in regard to the composition of the animal food consumed by man. It has been generally assumed that the effect of animal food, in human dietaries, is to in- crease the proportion of the nitrogenous constituents: from the results of these analyses, however, we can not escape the conclusion that the animal elements of a diet, as a whole, increase the proportions of the carbo-hydrates or non-nitrogenous constituents. It appears that two thirds of the nitrogen of the entire body, of the calf and bullocks, was found in the carcass, and of this twelve parts were in the bones, leav- ing fifty-four per cent of the whole nitrogen of the body in the soft parts of the carcass. Of the thirty-three per cent of the nitrogen of the entire body in the offal parts, it was estimated that in the calf seven to eight parts, and in the oxen four to five parts, would be con- sumed as human food. Of the total fat of the body, about seventy per cent in the calf, and rather more than seventy-live per cent in the oxen, were found in the carcass. Of the fat contained in the offal parts, it was estimated that five sixths in the calf and one fifth in the oxen would be consumed as human food. The percentage of the total ni- trogenous and total non-nitrogenous constituents of animals, included in the food of man, has been tabulated by Drs. Lawes and Gilbert as follows:
Per cent consumed as human food.
Of the total
of tho body.
Of the total fat of the body.
CO 60 50 50
According to this estimate, "there would be, in the fat calf ana- lyzed, \\ time, in the fat ox 2| times, in the fat lamb, fat sheep, and fat pig nearly 4| times, and in the very fat sheep 6^ times as much dry fat as dry nitrogenous constituents" in the parts of the animals consumed as human food. As one part of fat is equivalent to two and one half parts of starch, as a source of potential energy which must be taken as the measure of nutritive value, it will be necessary to estimate the fat in its equivalent as starch in making a comparison of vegetable and animal foods with reference to their nutritive value, and the rela- tive ratio of their nitrogenous and non-nitrogenous constituents. On this basis the results of the Rothamsted analyses have been tabulated as follows: RATIOS.
Proportion of dry fat to 1 of dry nitrogenous compounds.
Proportion of starch-equiva- lent of fat to 1 of dry nitrogenous compounds.
portions of the
portions of the
DESCRIPTION OF ANIMALS.
Store, lean and half -fat animals
Half-fat old sheep
Fat and very fat animals:
Very fat sheep
Store and half-fat animals . . .
Fat and very fat animals
Of the ten animals analyzed. .
For comparison with these ratios of the nutritive constituents of animal foods, wheat-flour hread was selected as one of the most im- portant of the representative articles of vegetable food. The fat in the bread itself, estimated at one per cent, which is probably above the average, was reckoned in its equivalent of starch, and the ratio of ni- trogenous and non-nitrogenous constituents was then found to be 1 to 6*8. Of the animals fattened for the butcher's use, the fat calf, only, gives a smaller proportion of non-nitrogenous constituents than the bread; the fat ox has nearly the same, and the other animals very much more. The averages also show that beef, mutton, and pork, on the whole, are not deficient in carbo-hydrates or non-nitrogenous nu- tritive constituents. After a full discussion of the subject, Drs. Lawes and Gilbert come to the conclusion that the great advantage of a mixed bread and meat diet, over one of bread alone, does not depend on the nitrogenous substance, but rather in substituting fat for a por- tion of the starch of vegetables. From the greater value of fat as a source of energy, and the general advantages of a variety of nutritive elements in the composition of a diet, this view of the influence of animal food seems to be well founded.
The limits of this article will not allow us to notice the experiments with sewage, and the feeding value of sewage-grown crops in the pro- duction of meat and milk; or the milling products of grain grown under a variety of conditions, and other special subjects of investiga- tion, that have been included in the work at Rothamsted..
It is perhaps worthy of notice that nitrogen was the prominent object of interest in the Rothamsted field experiments, whilo the carbo-hydrates or non-nitrogenous constituents of the food seemed to be the ruling elements in the feeding experiments. Is this apparent contrast in the materials required as leading factors in the economy of plants and animals a mere coincidence arising from the methods of investigation, or does it represent one of the correlations of organic life concerned in the conservation of energy? The mineral and ni- trogenous constituents of plants are taken up by their roots from the soil, which is almost, if not quite, the exclusive source of these ele- ments of plant-growth, while all of the carbon is elaborated by the leaves from the supplies in the atmosphere. The mineral and nitroge- nous constituents of the food of animals, on the other hand, are all discharged from the system, after performing their functions, in the liquid and solid excretions, and thus find their way to the soil, where they can be appropriated as plant-food; while a large proportion of the carbo-hydrates are exhaled in respiration as carbonic acid, the at- mospheric food of plants. By this constant circulation in their appro- priate channels the conservation of the nutrient elements, of both plants and animals, is fully maintained.
The legitimate objects of agricultural experiments are too often overlooked, and it is certainly a satisfaction, in a review of exj^eri- ments that have been systematically prosecuted for so many years, on such an extended scale, to find that they have been fully appreciated throughout the entire work. In one of the first reports of experiments at Rothamsted, on turnip-culture, published in 1847, it is said, "The object of the experiments has not been the production of immense crops, but *to trace, as far as we were able, the real conditions of growth required by the turnip, and to distinguish these from those of the crops to which it is, to a great extent, subservient." In this en- deavor to trace the laws which underlie the phenomena under inves- tigation, results of permanent value have been secured; and the prac- tical benefits, measured in pecuniary values, which have been derived from them are of greater importance from the fact that they are not merely empirical and detached facts that are true only under certain conditions, but have a foundation in principles of general application. Too often experiments are made in which the practical or pecuniary ends are the direct and immediate objects of inquiry, but such efforts, in the main, must result in disappointment, so far as any permanent interest is concerned, from the failure to trace the results obtained to their appropriate causes.
The work so well begun at Rothamsted is now carried on with undiminished energy, with a prospect of still more important results in the future. Dr. Lawes is now expending in his experiments more than 815,000 annually. A new building will be erected next year to relieve the laboratory from its accumulated stores of samples, that have a definite history and form the materials for future investigations. From five to nine hundred samples of the ash of experimental crops are collected each year, and with each sample of ash there is a dupli- duplicate plant that is dried and bottled. With the true spirit of an original investigator, who sees that there is more to be learned than has already been discovered, and with a modesty that well becomes one who has accomplished so much, Dr. Lawes (now Sir John Bennet Lawes) writes me: "We are getting greatly in arrears of what may be called published work, and both Dr. Gilbert and myself are much more interested in searching after the unknown than in making public what little we do know. I think, however, it is not right to keep back so much valuable matter, and I shall try and publish next year the whole series of our ash analysis, without comment of any sort, merely giving the history of the experiments in regard to manures, etc., so that the reader may be able to trace the remarkable changes which take place from time to time. You will see that we have got to a point in our experiments in which the mere growth of the crop is one item, and a very small one, in the scope of our inquiry; the relations of the crop to the manure and to the soil and atmosphere bring us face to face with problems of great difficulty, which require several life-times to elucidate."