SECTION I
THE GENERAL BIOLOGY OF BACTERIA AND THE TECHNIQUE OF BACTERIOLOGICAL STUDY °
CHAPTER I
THE DEVELOPMENT AND SCOPE OF BACTERIOLOGY
As we trace back to their ultimate origins the lines of development of living beings of the animal and plant kingdoms, we find them con- verging toward a common type, represented by a large group of uni- cellular organisms, so simple in structure, so unspecialized in function, that their classification in either the realm of plants or that of animals becomes little more than an academic question. However, even such microorganisms, in which the functions of nutrition, respiration, loco-* motion, and reproduction are concentrated within the confines of a single cell, and in which adaptation to special conditions more readily brings about modifications leading to the production of a multitude of delicately graded transitional forms, fall into groups which, either in structure or in biological attributes show evidence of a tendency toward one or the other of the great kingdoms.
Most important of these unicellular forms, for the student of medical science, are the bacteria and the protozoa.
The former, by reason of their undifferentiated protoplasm, their occasional possession of cellulose membranes, their biological tendency to synthetize, as well as to break down organic compounds, and because of the transitional forms which seem to connect them directly with the lower plants, are generally placed in the plant kingdom. The latter, chiefly on the basis of metabolism, are classified with the animals.
Knowledge of the existence of microorganisms as minute as the ones under discussion, was of necessity forced to await the perfection of instruments of magnification. It was not until the latter half of the seventcenth century, therefore, that the Jesuit, Kircher, in 1659, and the Dutch linen-draper, van Leeuwenhoek, in 1675, actually saw and
1 .
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described living beings too small to be scen with the naked eye. There can be no doubt that the small bodies seen by these men and their many immediate successors were, at least in part, bacteria. And indeed the descriptions and illustrations of several of the earliest workers cor- respond with many of the forms which are well known to us at the pregent day.
During the century following the work of these pioneers, the efforts of investigators lay chiefly in the more exact morphological description of some of the forms of unicellular life, already known. Conspicuous among the work of this period is that of Otto Friedrich Miiller. In the generation following Miiller’s work, however, a marked advance in the study of these forms was made by Ehrenberg,’ who established a classification which, in some of its cardinal divisions, is retained until the present day.
Meanwhile the regularity with which these “animalcula” or “in- fusion animalcula ” were demonstrable in tartar from the teeth, in intes- tinal contents, in well-water, etc., had begun to arouse in the minds of the more advanced physicians of the time a suspicion as to a possible relationship of these minute forms with The conception of “contagion,” or transmission of a disease from one human being to another, was, however, even at this time, centuries old. The fact had been recognized by Aristotle, had been reiterated by medieval philos- ophers, and had led, in 1546, to the division of contagious diseases by Fracastor, into those transmitted “per contactum,” and those con- veyed indirectly “per fomitem.” It was for these mysterious facts of the transmissibility of disease, that clinicians of the eighteenth century with remarkable insight, saw an explanation in the microorganisms dis covered by Leeuwenhock and his followers.
In fact, Plenciz of Vienna, writing in 1762, not only expressed a belief in the direct etiological connection between microorganisms and some dis , but was the first to advance the opinion that éach malady had its own specific causal g in the disc; the language of our modern knowledge of the subject, came ably near to the truth, not only as
but also in their suggestion of a specific therapy for ,
nt, which multiplied enormously
ed body. The opinions of this author, if translated iato ke
jon,
rds etiology and transmis:
zich disease,
The conception of a “contagium vivum ” was thus practically os-
tablished with the work of Plenciz and many others who followed in
+“ Die Infusionstierchen,” ete., Leipzig. 1838.
DEVELOPMENT AND SCOPE OF BACTERIOLOGY 3
his train, but the astonishingly shallow impression which the acute reasoning of, these men left upon the medical thought of their day furnishes an excellent example of the futility of the most penetrating speculation when unsupported by experimental data.
The real advancement in the scientific development of the subject was destined to be carried on along entirely different lines. In 1937, Schwann, a botanist, showed that the yeasts, found in fermenting sub- stances, were living beings, which bore a causal relationship to the proc- ess of fermentation. At almost the same time, similar observations were made by a French physicist, Cagniard-Latour. The opinions advanced by these men on the nature of fermentation aroused much interest and discussion, since, at that time and for a long period thereafter, fermentation wasascribed universally to proteid decomposition, a process which was entirely obscure but firmly believed to be of a purely chemical nature.
Although belief in the discovery of Schwann did not completely master the field until after Pasteur had completed his classical studies upon the fermentations occurring in beer and wine, yet the conception of a “fermentum vivum” aroused much speculation, and the attention of physicians and scientists was attracted to the many analogies ex- isting between phenomena of fermentation and those of disease.
The conception of such an analogy, however, was not a new thought in the philosophy of the time. Long before Schwann and Cagniard- Latour, the philosopher Robert Boyle, working in the seventeenth century, had prophesied that the mystery of infectious diseases would be aolved by him who should succeed in elucidating the nature of fermenta- tion.
Nevertheless, the diligent search for microorganisms in relation to various diseases which followed, led to few results, and the successes whieh were attained were limited to the diseases caused by some of the larger fungi, favus (1839), thrush (1839), and pityriasis versicolor (1846). During this time of ardent but often poorly controlled etiolog- ical research, it was Henle who formulated the postulates of conserva- tism, almost as rigid as the later postulates of Koch, requiring that proof of the etiological relationship of a microorganism to a disease could not be brought merely by finding it in a lesion of the disease, but that constant presence in such lesions must be proven and isolation and study of the microorganism away from the diseased body must be car- ried out.
It was during this period also that one of the most fundamental!
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questions, namely, that of the origin of these minute living beings, w being discussed with much passion by the scientific world. It was he by the conservative majority that the microorganisms described b Leeuwenhoek and others after him, were produced by spontaneou generation. The doctrine of spontaneous generation, in fact, wa solidly established and sanctified by tradition, and had been appliec in the past not alone to microorganisms.’ And it must not be forgotten that without the aid of our modern methods of study, satisfactory proof for or against such a process was not easily brought.
Needham, who published in 1749, had spent much time in fortii ing his opinions in favor of spontaneous generation by extensive e3 perimentation. He had placed putrefying material and vegetable in- fusions in sealed flasks, exposing them for a short time to heat, by immersing them in a vessel of boiling water, and had later shown them to be teeming with microorganisms. He was supported in his views by no less an authority than Buffon. The work of Needham, however, showed a number of experimental inaccuracies which were thoroughly sifted by the Abbé Spallanazani. This investigator repeated the cx- periments of Needham, employing, however, greater care in scaling his flasks, and subjecting them to a more thorough exposure to heat. His results did not support the views of Needham, but were answered by the latter with the argument that by excessive heating he had pro- duced chemical changes in his solutions which had made spontaneous generation impossible.
The experiments of Schulze, in 1836, who failed to find living crgan- isms in infusions which had been boiled, and to which air had been admitted only after passage through strongly acid solutions, and similar results obtained by Schwann, who had passed the air through highly heated tubes, were open to criticism by their opponents, who claimed that chemical alteration of the air subjected to such drastic influences, had been responsible for the absence of bacteria in the infusion. Similar experiments by Schroeder and Dusch, who had stoppered their flasks with cotton plugs, were not open to this objection, but had also failed to convince. The question was not definitely settled until the years im-
'Valleri-Radot, in his life of Pasteur, stated that Van Helmont, in the six- teenth century, had given a celebrated prescription for the creation of mice from dirty linen and a few grains of wheat or pieces of cheese. During the centu- ries following, although, of course, such remarkable and amusing beliefs no longer held sway, nevertheless the question of spontaneous generation of minute and structureless bodies, like the bacteria, still found learned and thoughtful partisans,
DEVELOPMENT AND SCOPE OF BACTERIOLOGY 5
mediately following 1860, when Pasteur conducted a series of experi- ments which were not only important in incontrovertibly refuting the doctrine of spontaneous generation, but in establishing the principles of scientific investigation which have influenced bacteriological re- search since his time.*
Pasteur attacked the problem from two points of view. In the first place he demonstrated that when air was filtered through cotton- wool, innumerable microorganisms were deposited upon the filter. A single shred of such a contaminated filter dropped into a flask of pre- viously sterilized nutritive fluid, sufficed to bring about a rapid and luxuriant growth of microorganisms. In the second place, he succeeded in showing that similar, sterilized “putrescible” liquids, if left in con- tact with air, would remain uncontaminated provided that the en- trance of dust particles were prohibited. This he succeeded in doing by devising flasks, the necks of which had been drawn out into fine tubes bent in the form of a U. The ends of these U-tubes, being left open, permitted the sedimentation of dust from the air as far as the lowest angle of the tube, but, in the absence of an air current, no dust was carried up the second arm into the liquid. In such flasks, he showed that no contamination took place but could be immediately induced by slanting the entire apparatus until the liquid was allowed to run into the bent arm of the U-tube. Finally, by exposing a series of flasks containing sterile yeast infusion, at different atmospheric levels, in places in which the air was subject to varying degrees of dust con- tamination, he showed an inverse relationship between the purity of the air and the contamination of his flasks with microorganisms.
The doctrine of spontaneous generation had thus received its final refutation, except in one particular. It was not yet clear why com- plete sterility was not always obtained by the application of definite degrees of heat. This final link in the chain of evidence was supplied, some ten years later, by Cohn, who, in 1871, was the first to observe and correctly interpret bacterial spores and to demonstrate their high powers of resistance against heat and other deleterious influences.
‘In a letter to his foremost opponent, at this period, Pasteur writes: “In experimental science, it is always 8 mistake not to doubt when facts do not compel affirmation.”
The critical spirit pervading the scientific thought of that time in France is also well expressed by Oliver Wendell Holmes, who said that he had learned three things in Paris: “Not to take authority when I can have facts, not to guess when T can know, and not to think that a man must take physic because he is sick.”
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Meanwhile, Pasteur, parallel with his researches upon spontaneous generation, had been carrying on experiments upon the subject of fermentation along the lines suggested by Cagniard-Latour. As a
- consequence of these experiments, he not only confirmed the opinions both of this author and of Schwann concerning the fermentation of beer and wine by yeasts, but was able to show that a number of other fer- mentations, such as those of lactic and butyric acid, as well as the de- composition of organic matter by putrefaction, were directly due to the action of microorganisms. It was the discovery of the living agents underlying putrefaction, especially, which exerted the most active influence upon the medical research of the day. This is illustrated by Lister’s work. The suppurative processes occurring in infected wounds had long been regarded as a species of putrefaction, and Lord Lister, working directly upon the premises supplied by Pasteur, introduced into both the active and prophylactic treatment of surgical wounds, the antiseptic principles which alone have made modern surgery possible.
There now followed a period in which bacteriological investigation was concentrated upon problems of etiology. Stimulated by Pasteur’s successes, the long-cherished hope of finding some specifie microorgan- ism as the causal agent in each infectious disease was revived.
Pollender, in 1855, had reported the presence of rod-shaped bodies in the blood and spleen of animals dead of anthrax. Brauell, several years later, had made similar cbservations and had expressed definite opinions as to the causative relationship of these rods to the disease. Convineing proof, however, had not been brought by cither of the: observers. Finally, in 1863, Davaine, in a series of brilliant investi- gations, not only confirmed the observations of the two authors men- tioned above, but succceded in demonstrating that the disease could be transmitted by means of blood containing these rods and could never be transmitted by blood from which these rods were absent. Anthrax, thus, is the first disease in which definite proof of bacterial causation was brought.
Speaking before the French Academy of Medicine at this time, Davaine suggested that the manifestations of the discase might in reality represent the results of a specifie fermentation produced by the bacilli he had found. This, in a crude way, expresses the modern conception of infectious disease.
Within a few years after this, 1868, the adherents of the parasitic theory of infectious diseases were further encouraged by the di by Obermeier, of a spirillum in the blood of patients suffering from
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DEVELOPMENT AND SCOPE OF BACTERIOLOGY 7
relapsing fever. It is not surprising that the successes attained in these diseases, fostering hope of analogous results in all other similar condi- tions, but without the aid of adequate experimental methods, should have led to many unjustified claims and to much fantastic theorizing. Thus Hallier, at about this time, advanced a theory as to the etiology of infectious diseases, in which he attributed all such conditions to the moulds or hyphomycetes, regarding the smaller form or bacteria as developmental stages of these more complicated forms. Extravagant conjectures of this kind, however, did not maintain themselves for any length of time in the light of the critical attitude which was already pervading bacteriological research.
Progress was made during the years immediately following, chiefly in the elucidation of suppurative processes. Rindfleisch, von Reckling- hausen, and Waldeyer, almost simultaneously, described bodies which they observed in sections of tissue containing abscesses, and which they believed to be microorganisms. Notable support was given to their opinion by similar observations made upon pus by Klebs, in 1870. In view, however, of the purely morphological nature of thcir studies, the opinions of these observers did not entirely prevail. Satisfactory methods of cultivation and isolation had not yet been developed, and Billroth and his followers, with a conservatism entirely justified under existing conditions, while admitting the constant presence of bacteria in purulent lesions, denied their etiological significance. The contro- versy that followed was rich in suggestions which greatly facilitated the work of later investigators, but could not be definitely settled until 1880, when Koch introduced the technical methods which have made bacteriology an exact science. By the use of solid nutritive media, the isolation of bacteria and their biological study in pure culture were made possible. At about the same time the use of anilin dyes, developed by Weigert, Koch, and Ehrlich, was introduced ‘nto morphological study and facilitated the observation of the finer structural details which had been unnoticed while only the grosser methods employed for tissue staining had been available.
With the publication of Koch’s work, there began an era unusually rich in results held in leash heretofore by inadequate technical methods. The discovery of the typhoid bacillus in 1880, of the bacillus of fowl cholera and the pneumococcus in the same year, and of the tubercle bacillus in 1882, initiated a series of etiological discoveries which, ex- tending over not more than fiftcen years, elucidated the causation of a majority of the infectious discases,