Popular Science Monthly/Volume 6/February 1875/Bacteria and their Effects
|BACTERIA AND THEIR EFFECTS.|
LIVING organisms, microscopical in size, of the simplest, most elementary nature, and moving freely in different liquids, have been known to observers for nearly two hundred years. Scientific classification and description were long impossible, on account of the meagre facilities furnished by the microscopes of the last century; but, during the last fifty years, the means of observation have been so much improved, and the number of observers has been so great, that the advance in our knowledge of microscopical bodies compares favorably with that in other branches of science. This advance has been greatly stimulated by a tendency to see in low vegetable or animal organisms the exciting cause not only of fermentation and decomposition, but also of many diseases. Pasteur's researches into the nature and causes of fermentation, the lectures and publications of Tyndall and Huxley, and the bitter discussions about spontaneous generation, have made us all familiar with the names bacteria, vibriones, and micrococci, or microzymas, with which we associate the idea of microscopical
Fig. 1.—a, Micrococci; d, Micrococci, multiplying by scission: b, c. Bacteria (rod Bacteria, B. termo; e, vibriones; f, h, i, k, Torulæ, or Yeast-Plant, sprouting; g, probably "Dauersporen," durable or resting spores.
bodies, round, oval, or rod-like and jointed, varying in length from five ten-thousandths to one one-hundredth of a millimetre, and found especially in putrefying vegetable and animal infusions. The term micrococcus has always been restricted to the small, round, or ovoid bodies, but bacterium and vibrio have been applied indiscriminately to all, the former being more commonly used in France and Germany, the latter in England. When used in the narrower sense, bacteria denotes stiff, rod-like bodies, single or jointed, motionless or endowed with an oscillatory movement in place, while vibrio is applied to those which move rapidly across the field of the microscope with an undulatory, sinuous motion. Another variety, less frequently found, is larger, and has the form of a corkscrew, with from one and one-half to three or even four complete turns. These spiral forms are perfectly rigid, and rotate about their long axis with great rapidity, moving rapidly forward and backward with the regularity, although not the deliberation, of a pendulum. Their rotation about the long axis gives rise to the appearance of a wavy, serpent-like motion, which has deceived many observers, and it is very probable that the smaller vibriones mentioned above owe their apparent sinuous motion to the same cause. The ease with which one may be deceived on such a point will be readily understood by any one who has noticed a large screw in motion, or the shadow of a slowly-turning corkscrew.
Leeuwenhoek, a Dutchman, published, in 1684, the earliest observations of bacteria of which we have any record. He found them chiefly in the matter picked from between his own teeth and those of his acquaintances, and, animated apparently by the same spirit for which his countrywomen are so noted, he defends himself against a possible charge of uncleanliness by mentioning that he habitually brushed his teeth after every meal; but he also records that he found the largest quantity of bacteria between the uncared-for, broken teeth of an old man. He supposed these bacteria to be animals, and, indeed, gave the name eels to some large ones which he found in vinegar, whose motions were so active that he was "obliged to kill one before the limner could portray it." In the eighteenth century Müller made a classification of the forms then known, but it was not until after the great improvements made in the construction of microscopes, about 1820, that Ehrenberg gave the complete description and classification which have served almost until the present day. His book ("Infusionsthierchen") was published in 1838. The different forms were grouped in one family, the Vibrionidæ, and, as the title shows, were still supposed to be animals.
To-day they are known to be plants, and the different varieties are supposed by many observers to represent only different periods of development. Robin asserted several years ago that the ordinary rod bacteria could develop into the long thread bacteria, and even into the long filaments of leptothrix found so constantly in the mouth; but this was not generally believed, and the latest complete classification, that of Ferd. Cohn, published in 1872, is based upon the absence of such a developmental relationship. The study of these plants is rendered very difficult by their extreme smallness, and all attempts to cultivate them under the microscope, in "wet chambers," have failed to disclose the secrets of their growth, on account of the abnormal conditions in which they are necessarily placed. A considerable depth of liquid seems to be essential, as do also the presence of air, and protection against shocks or jars, and movement of the liquid; consequently, they can be studied only by comparing the forms found at intervals during a long period of time, either when cultivated artificially, or when growing spontaneously under natural conditions.
In this way Billroth, who has published the most recent and, in many respects, the most remarkable work upon the subject, was able to make out the whole series of changes, from the spore to the long filaments, by using for his observations the yellowish mould which formed on the wall of his laboratory, where the water leaked slowly from a loose faucet. At the same time he discovered the nature and importance of certain glistening spherical bodies frequently found in infusions containing bacteria, and called Dauersporen, or durable spores (Fig. 1, g), by Cohn, although he did not think bacteria were developed from them. Billroth demonstrated that these Dauersporen
form micrococci in their interior, which are set free by the bursting of the envelope, and are then capable of multiplication by scission, or of lengthening into bacteria; also, that they are endowed with great vitality, and are not destroyed by freezing, boiling, or drying. He had some which germinated after they had been kept dry for eight years; and, whenever he wished to make sure of the destruction of the spores contained in his experimental liquids, he heated them to 392° Fahr.
They are formed in the interior of bacteria, and sink to the bottom of the liquid which contains them. The importance of these facts in their bearing upon the question of spontaneous generation, and upon the innumerable repetitions and variations of the experiments with sealed flasks, which have attracted so much attention since Pasteur made them, cannot be over-estimated; for, as Prof. Wyman, of Cambridge, says, "The issue between the advocates and opponents of the doctrine in question" (spontaneous generation) "clearly turns on the extent to which it can be proved that living beings resist the action of water at a high temperature."—American Journal of Science and Art, September, 1867.
Bacteria themselves are much more easily affected by heat and cold than are these Dauersporen. Their motions cease when the temperature is reduced nearly to the freezing-point; but it may be carried even below zero, and yet the movements will recommence as soon as it is raised again above 40° or 45°. Exposure to a temperature of 140° will kill them; but this result seems to depend quite as much upon the length of time during which they are exposed to it, as upon the degree of heat itself, several hours being required for the lesser degrees, while ten to fifteen minutes, at boiling heat, are sufficient, and even four or five at 215°.
In the air, bacteria, or bacteria-spores, exist, but only in moderate numbers, for exposure to the air often fails to cause cloudiness of artificial nutritive liquids, when the plants that existed in them before-hand have been destroyed by heat; and sometimes portions of meat taken from a recently-killed animal, with all possible precautions to prevent inoculation with bacteria through the instruments employed, and placed in open vases that have been washed in alcohol and then scorched in a hot flame, remain for days and weeks without putrefying. They are present in all kinds of water, and generally in considerable numbers. Cohn found them in the vapor condensed upon the inner surface of a bell-glass placed over a dish of water; and it is probable that those found in the air are enabled to live by the moisture contained in it. Their presence in the liquids and tissues of the body, often affirmed and denied, is now proved beyond question, Billroth's experiments on this point having been repeated and confirmed very recently by Tiegel. Rapid multiplication in the living body is prevented in part by the motion of the blood, and in part by the vital energy of the tissues, which is so vigorous that these plants cannot check it, and thereby obtain the nourishment needed for their own growth; but, when life has ceased, or when an abnormal condition of the tissues has been brought about by any cause, then rapid growth begins, and we have, in the one case, putrefaction; in the other, various pathological changes of more or less importance.
About the year 1865, two physicians of Strasburg, Messrs. Coze and Feltz, published a series of experiments which they had made with inoculations of putrid matter; and in 1872 they published a book upon the same subject, claiming that the virulent effects of putrid matter were due to the presence and growth of bacteria, and that the blood of an animal poisoned with such matter was itself virulent to a high degree, and that this virulence was increased by successive inoculations. A similar series of investigations had led another French physician, Davaine, to the opinion that the disease called anthrax, when it occurs in animals, and malignant pustule when it affects man, was caused by a certain variety of bacteria, to which he gave the name bacteridia.
Davaine repeated the experiments of Coze and Feltz, and in September, 1872, read before the Académie des Sciences, in Paris, a report of three series of inoculations with putrid blood, the results of which were so startling that for several months the discussions in the Academy turned almost exclusively upon the subject of septicæmia, or blood-poisoning. The first series showed that inoculation of a rabbit with a drop of blood, putrefied in the open air, rarely killed the animal, and that sometimes ten or fifteen drops were necessary. The second series comprised successive inoculations of blood from one septicæmic animal to the next, and showed that 1⁄10 to 1⁄100 of a drop was sufficient to kill the fifth, 1⁄10000 1⁄20000 would kill the tenth, while, for the twenty-fifth, the one-ten-trillionth part of a drop was fatal.
Incredible as some of these assertions seemed, they were verified by many experimenters; but the minimum dose that would certainly kill was placed at the one-millionth part of a drop. Davaine claimed that the active poisonous principle was the bacterium, which, by its growth and multiplication in the blood, acted as a ferment; and this opinion, supported by Pasteur, was generally accepted, and it was supposed that the ordinary acute inflammatory complications of wounds, accompanied by symptoms of general poisoning, were caused by the accidental entry of bacteria. The same opinion had been held before, and the novelty of Davaine's views lay chiefly in the excessive minuteness of the quantity necessary to produce the effect.
The chief benefit derived from these experiments and discussions in Paris was found in the great interest which was excited everywhere in the question. The experiments were repeated, and the conclusions examined in almost every pathological laboratory in Europe, and we have every reason to expect that, through this general examination and discussion, the truth will appear. From time to time articles appeared denying the virulence claimed for bacteria; the earliest of these was a paper submitted to the Académic des Sciences, in April, 1873, by M. Onimus, who had been experimenting under the direction of Prof. Robin. He placed putrefying blood in a bag made of a dialytic membrane, and immersed the whole in distilled water, which, after a few hours, was found to be filled with bacteria. Inoculation with the blood produced the usual results, but inoculation with the water caused no septic symptoms whatever; on the other hand, the same blood, when subjected to various processes which removed or destroyed the bacteria, retained its virulence, and from these experiments he drew the conclusion that the virus of putrid infection is not an organized ferment, not bacteria, but an albuminoid substance. Panum, who held similar views twenty years ago, has reasserted his belief in them in an article published in Virchow's Archives, for July, 1874, and during the last year the weight of testimony has all been in this direction. Clinical observation has been employed to confirm or refute the conclusions of experimental pathology, and has clearly demonstrated that the poisonous processes, of which we have spoken, can begin in the human body and proceed without the presence of bacteria, and that bacteria may be present in large quantities without the slightest symptom of any poisonous complication.
It is probable that their rôle, so far as disease is concerned, is as follows: While they have no power in themselves to excite disease (diphtheria, vaccinia, septicæmia, typhoid fever, etc.), they are able to absorb the poison (ferment?) which is capable of producing it, to "fix" it, as it is termed, and to give it up to any tissue with which they may come into contact, acting thus as carriers of contagion; then, after the abnormal process has been commenced in the body, a change is brought about in the tissues which renders them suitable for the rapid growth and multiplication of the bacteria, which, in turn, augment the change in the tissues, and thus there is formed a vicious circle, the consequences of which are too often fatal.
Any agent which destroys the life of the bacteria, or prevents their multiplication, breaks this circle and renders a cure possible.
The influence of bacteria in fermentation is still undecided, but, for the sake of completeness, the different opinions should be mentioned. It is admitted by all chemists that these or similar organisms are invariably present in some fermentations—Bacterium termo, or rod bacterium, in putrefaction, and the yeast-plant in alcoholic fermentation, for example; and while some claim that the process is due to the vitality and growth of these plants, others hold that this growth is an effect, not, a cause; and a third party claim that the plants secrete the actual ferment.
According to Liebig, fermentation is an action which is produced in a fermentable substance by an albuminous matter which is dead and in spontaneous decomposition; that is, fermentation is a correlative phenomenon of death. On the other hand, Pasteur maintains that fermentation occurs only when a microscopical vegetable organism nourishes itself and multiplies at the expense of a part of the fermentable substance. All fermentation is accompanied by life; both processes (fermentation and growth) begin and end simultaneously; that is, fermentation is a correlative phenomenon of life.
The question of spontaneous generation is closely bound up with the question of fermentation, the supporters of the former claiming that life has its origin in a new combination of elements—archebiosis, a combination which resembles that which occurs in crystallization, and that the same causes which induce the chemical decompositions and subsequent combinations known as fermentation also bring about the combinations which result in life. The discussion has been very active, and, in France, Pasteur, skillful dialectician as he is, had to fight long and hard for the victory which he won. History shows that spontaneous generation has often been invoked to explain an unknown mode of production of life, and has always disappeared before advancing knowledge, and, now that it has been overthrown when claimed for the lowest forms of microscopical life, it probably will not reappear until an advance in the means of observation shall have revealed to observers still lower and more minute forms.