Popular Science Monthly/Volume 83/December 1913/Alcohol from a Scientific Point of View II

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II. The Relative Toxicity of the Various Alcohols



IN a previous study on "The Discovery and Nature of Alcohol,"[1] we have seen that the various alcohols differ among themselves as to their molecular weights and boiling points. These two differences characterizing the alcohols are associated further with a difference in toxicity or poisonous effect. This we shall now consider.

The relation between the molecular weight of a substance and its toxicity was seen as early as 1837 by Black, but it was not until more than a quarter of a century later that Rabuteau was able to generalize this relationship. In his study of the metals he observed that the higher the molecular weight and boiling point, the greater the toxicity. This law experiment has shown often to be in default for the metals. For the alcohols, on the other hand, it has a striking application.

If greater toxicity be associated with a higher molecular weight and boiling point, it would follow that an alcohol such as amyl, with 88 atoms to the molecule and a boiling point of 138° C, would be more poisonous than ethyl alcohol with 46 atoms to the molecule and a boiling point of 78.4° C. Such, in fact, was early shown to be the case. But it may be objected that the difference between the two is extreme. It would be more convincing if two alcohols, such, for example, as ethyl and methyl, closely approximating in molecular weights and boiling points, complied with the law.

To a comparison of these we shall return.

We shall first consider the experimental evidence which has given to us a measure of the exact toxicity of the various alcohols.

Early Experiments on the Toxicity of Alcohol

Fr. Petit, who was among the first to busy himself with the study of the toxic effects of alcohol, showed that if alcohol is injected into the veins of an animal, a rapid death ensues. Following this simple experiment a considerable period of time elapsed before the subject was again taken up. The next work recorded is that by two Italian physiologists, Lussana and Albertoni.

These investigators, by a series of interesting experiments, estimated that 6 grams of pure alcohol for each kilogram of body weight is a lethal or killing amount when injected into the stomach of an animal.

This was the beginning of quantitative work to which a few years later Dujardin-Beaumetz and Audigé added a brilliant series of experiments. They studied not only the toxicity of ethyl alcohol, but also that of other alcohols as well. Briefly stated, the question that they proposed to themselves was: How much alcohol is necessary to kill a kilogram of living matter in less than thirty-six hours?

If, for example, in studying the toxicity of alcohol, we find that 77.5 grams of alcohol injected into the stomach of an animal of 10 kilograms weight produces death in less than 36 hours, the question then as to the amount necessary to kill per kilogram is easily determined, for if 77.5 grams kill the entire 10 kilograms, 7.75 grams is the amount necessary to kill per kilogram. This, in fact, was the amount of ethyl alcohol found by them to be the lethal dose. This amount, however, is considerably below the estimate of 6 grams by Lussana and Albertoni. This difference in amount may be explained in part by the difference in the time limit employed; for while 6 grams may eventually kill, 7.75 grams is necessary to kill within a limited period of thirty-six hours.

For the coefficient of toxicity of the higher alcohols, Dujardin-Beaumetz and Audigé found the following values: For propyl, the member of the series just above ethyl, 3.75 grams per kilogram; for butyl 1.85, and for amyl 1.50 to 1.60 grams per kilogram body weight.

The molecular weight, boiling point and relative toxicity of the alcohols of fermentation are briefly summarized in the following table:

Alcohol Molecular Weight Boiling Point[2] Relative Toxicity
Ethyl 46 78° C. 7.75 gr. per kg.
Propyl 60 97.0° C. 3.75 gr. per kg.
Butyl 74 117.0° C. 1.85 gr. per kg.
Amyl 88 138.0° C. 1.50 to 1.60 gr. per kg.

From this table it is to be seen that the higher the molecular weight and boiling point, the smaller is the amount required to kill a kilogram of living matter. In other words, the higher an alcohol is in molecular weight and boiling point, the greater is its toxicity. This, as we have seen, is the law of Rabuteau with which the above facts of experiment are in direct accord.

In a study of methyl alcohol, on the other hand, Dujardin-Beaumetz and Audigé concluded that the toxicity is not in keeping with the law of Rabuteau. Though methyl alcohol has a molecular weight of 32 and a point of ebullition of about 66° C.—in both lower than ethyl alcohol—yet its toxicity was found by them to be greater—7 grams being sufficient to produce death per kilogram, while, as we have seen, 7.75 grams of ethyl alcohol were required.

But the methyl alcohol of the time of Dujardin-Beaumetz and Audigé, as we now know, was far from pure—hence the failure to gain an accurate measure of its toxicity. To-day that methyl alcohol is produced in greater purity, we should be able to retest the question with greater accuracy. To this we shall soon return.

From the investigations of Dujardin-Beaumetz and Audigé we have, then, our first experimental evidence that while alcohols in large doses are poisonous, not all alcohols are equally poisonous. To them is also due the credit of showing that for the alcohols of fermentation the toxicity is directly in proportion to the molecular weight and boiling point; in other words, that they are in accord with the law of Rabuteau—the higher the molecular weight and boiling point, the greater the toxicity.

Difficulties Confronting Investigation of Toxicity

Concerning the difficulties confronting investigation in this subject, we have said nothing. Some of these we shall now consider.

Observation has been made by various investigators that different animals react differently to poisonous substances. From this observation arose the discussion as to "the choice of animal" best suited to a study of alcoholic poisoning. Morgan, who had experimented upon the dog, argued that it was the most acceptable animal for work of this sort. Laborde, who, on the other hand, had studied the guinea-pig, urged the use of this animal; while Colin (who had studied neither) was of the impression that the horse or the cow would be more susceptible than either. Daremburg, in considering the discussion, hopefully suggested that probably another contradictor would recommend either the giraffe or the elephant. This in fact might have been the plight had not the work of Joffroy and Serveaux appeared.

Joffroy and Serveaux have shown that while animals differ in susceptibility according to their kind, this difference is relatively constant and usually but slight. The choice of animals thus becomes, in great part, important in so far as one animal rather than another serves better the purpose of this or that investigator.

A question of more than passing importance in the measure of toxicity, however, is the method of administering the substance to be tested. It is a well-known fact that some substances which are extremely poisonous when injected under the skin, for example, snake venom, are in no sense poisonous when given by the stomach. On the other hand, other substances which show slight poisonous effects if given subcutaneously, act with extreme rapidity if added directly to the blood stream. These facts give to the ways and means of injection a high importance.

The difficulties in the way of injection may now be considered more fully. A lethal dose of alcohol injected into the stomach or under the skin of an animal becomes lethal only after it has been absorbed into and distributed by the blood stream. Hence the importance of knowing whether the alcohol is absorbed promptly so as not to undergo loss or change in the tissues. In a word the rate of absorption must be rapid.

If also by injecting a lethal amount of alcohol under the skin or into the muscles, serious secondary injuries, such, for example, as abscesses and the like, result, a source of error is possible; for a dose of alcohol under the toxic equivalent aided by these secondary influences might thus produce death.

It was evident to Joffroy and Serveaux that in order to prevent errors arising from the rate of absorption and to reduce to lowest terms the danger of secondary injuries, a method should be employed which would insure that the entire amount of alcohol be in the blood at the same time. This could be accomplished in only one way, that was by adding the alcohol directly to the blood stream. They therefore turned their attention to intravenous injections.

While this method of adding the alcohol directly to the blood stream would control the rate of absorption and largely allay secondary injuries, yet it was found productive of errors the overcoming of which was imperative to an accurate measure of toxicity. In the first place it has been shown that if alcohol be injected too rapidly injuries both to the veins and to the viscera arise. On the other hand, if it be added too slowly, a loss of alcohol may occur through the kidneys and other ways of elimination.

The first problem of Joffroy and Serveaux was to find a way by which the injection could be made at constant pressure. This was accomplished by substituting for the Hypodermic syringe which had been generally used the "flaçon de Mariotte." This gave a constant pressure which was easily regulated at any time during the experiment. By injecting one cubic centimeter per minute for each kilogram of body weight they found no injury occurring either to the veins or to the viscera. With this rate it was also found that the entire amount could be injected before any considerable time had elapsed for elimination to take place.

With the error of rate of injection thus controlled they were ready to try the measure of toxicity. A series on rabbits gave discouraging extremes varying from 4.33 to 13.18 cubic centimeters per kilogram necessary to kill.[3] With variations so great as nearly 3 to 1 it was evident that the method was far from perfect. What in the method caused so great a variation?

An examination of animals that had died from small amounts demonstrated that death had been due to coagulation and to a consequent blocking of the blood stream. They then set about for a solution of the more serious problem—the prevention of coagulation. First, tests with various salts were made. But these were found to be of no service since a salt in order to be a non-coagulant had to be of sufficient strength itself to be toxic.

A second study hit upon an ingenious method of procedure. It has long been known that the blood of animals ingested by leeches is prevented from coagulation (in the body of the leech) by an anticoagulant. Haycroft demonstrated that an alcoholic extract of the buccal cavity of leeches injected into the arteries of rabbits or dogs prevents coagulation of the blood, and at the same time is productive of no observable injury. Joffroy and Serveaux determined upon testing its powers to prevent coagulation in a normal salt solution.

It is evident that the addition of so complex a substance as leech-extract to the blood of an animal must be made only with the most careful control. Two things were demanded of it: (1) It must serve its purpose,in this case prevent coagulation; (2) it must in no way injure the animal. In testing for its injurious effects it was found that the injection of enormous quantities[4] produced no injury. Since no coagulation followed they were in possession of an anticoagulant by the aid of which they could test the toxicity of a substance added directly to the blood stream.

Later Experiments and Units of Measure

(a) The Experimental Toxic Equivalent

Joffroy and Serveaux established as a convenient unit of measure the amount of alcohol that would kill per kilogram while the experiment was in progress. This they called the experimental toxic equivalent. This limit, as is evident, has the advantage of greater rapidity than that (36 hours) used by Dujardin-Beaumetz and Audigé. By injecting the alcohol and this anticoagulant into the blood, in a series of eight experiments, the following amounts of alcohol were found sufficient to kill per kilogram of body weight: 12.65 c.c, 12.18, 11.69, 10.32, 10.51, 11.99, 12.48, 11.70. This series shows a striking regularity with extremes varying only between 10.32 and 12.65 c.c., variations which would be readily accounted for by differences in age, race and the like of the rabbits used.

For ethyl alcohol, then, these authors have demonstrated that 11.69 c.c. (9.36 gr.) is the amount sufficient to produce death during the operation, that is, it is the experimental toxic equivalent.

For methyl alcohol, which Dujardin-Beaumetz and Audigé had found more toxic than ethyl, the results of Joffroy and Serveaux are most interesting. Although the method of purification had been greatly improved since the time of Dujardin-Beaumetz and Audigé, yet methyl alcohols coming from different sources were still shown to vary in their poisonous effects. Thus three alcohols from different sources gave the coefficient of toxicity for the rabbit as follows:

23.75 c.c. per kg.

26.75 c.c. per kg.

25.55 c.c. per kg.

As an average of these three series we have an experimental toxic equivalent of 25.35 c.c. for methyl alcohol. The point of interest is not the degree of variation present, but the relatively slight toxicity of methyl alcohol when compared with ethyl alcohol. We shall see that the same is true when we study this as measured by another toxic limit.

For the entire series of primary alcohols which we have considered—methyl, ethyl and the higher alcohols—the following table summarizes the experimental toxic equivalent and its relation to molecular weight and boiling point.

Chemical Formula Molecular Weight Boiling Point Expt. Toxic
Methyl 32 66.0° C. 23.35 c.c.
Ethyl 46 78.4° C. 11.70 c.c.
Propyl 60 97.0° C. 3.4 c.c.
(Iso)-Butyl 74 117.0° C. 1.45 c.c.
Amyl 88 138.0° C. 0.36 c.c.

Such are the results when death is produced while the experiment is in progress. While this method has the advantage of rapidity it has also disadvantages.

It is clear that by adding alcohol up until the last inspiration more alcohol is given than is necessary to produce death. For this reason Joffroy and Serveaux realized that the experimental toxic equivalent has only a comparative value. For the exact measurement of toxicity the question is not how much alcohol will kill while the experiment is in progress, nor yet within a limit of 36 hours. The one question is, What is the amount necessary to kill?

(b) The True Toxic Equivalent

The amount necessary to kill may be determined in one of two ways: (1) By giving for a long period of time small amounts which will finally produce death, or (2) by giving at one time an amount sufficient to produce}} death within a brief delay. The second method was selected for experimentation. This amount was designated the true toxic equivalent.

By experiment it was found that for the dog when an amount less than 7.90 c.c. of commercially pure ethyl alcohol was given recovery followed, at or above 8 c.c. per kilogram death ensued. For the dog, hence, the true toxic equivalent was set as 7.95 c.c. (6.36 gr.). For the rabbit from amounts lower than 7.50 c.c. all survived; from amounts above 7.80 c.c. all died. For the rabbit, therefore, 7.75 c.c. (6.20 gr.) per kilogram was set as the true toxic equivalent. The average of 6.36 gr. for the dog, while seemingly differing considerably from that (7.75 gr.) found by Dujardin-Beaumetz and Audigé is in fact in close accord with it.

If in the experiments of Dujardin-Beaumetz and Audigé all animals that died within three or four days are substituted for all animals that died within 36 hours, the toxic equivalent for ethyl alcohol instead of being 7.75 gr. increases to about 6 gr. per kilogram. This is in agreement with what Lussana and Albertoni found, but it is slightly higher than that given by Joffroy and Serveaux (6.36 gr.) in the perfected method.

The work by Joffroy and Serveaux on the true toxic equivalent of methyl alcohol is most thorough. By the same procedure as for ethyl alcohol they have shown that for the dog amounts above 9.10 c.c. produce death. They have, therefore, established as the true toxic equivalent for the dog by intravenous injection 9 c.c. per kilogram. For the rabbit this is 10.90 c.c. per kilogram.

Two things of interest are made evident in the work on methyl alcohol. These are: (1) That for the dog methyl alcohol is more toxic than for the rabbit (the opposite was seen to be true for ethyl); (2) that for both the dog and the rabbit it is less toxic than ethyl alcohol, and is therefore in harmony with the law of Rabuteau.

From these various studies it is clear that alcohol in large quantities is a poison capable of causing death, the most toxic being amyl and the least toxic[5] methyl, and that the difference in the degree of toxicity follows the law of Rabuteau: A substance (alcohol) is as toxic as its molecular weight and boiling point are elevated.

  1. Pop. Sci. Mo., p. 567, June, 1913
  2. The boiling points are taken from Meyer and Jacobson's "Lehrbuch der organischen Chemie," Bd. I., 1906, p. 209.
  3. The exact amounts were as follows: 4.32 c.c, 8.92, 7.26, 12.18, 6.35, 8.44, 4.90, 7.54 c.c. per kilogram.
  4. 1,185 c.c.—nearly 600 grams per kilogram—was injected; of this some was lost, but 425 grams per kilogram remained.
  5. This does not take into account the latent ill-effects on man shown to be characteristic of methyl alcohol.