Part 24

2. Contagious also by atmospheric transmission through short distances.

Variola, Varioloid, Varicella, Measles, Diphtheria, Scarlatina, Rötheln, Mumps, Whooping Cough, Typhus, Relapsing Fever.

3. Endemic, occasionally epidemic.

Malarial Fevers (Intermittent, Remittent, and Pernicious Fever), Dengue, Yellow Fever.

4. Other zymotic or enthetic diseases.

Influenza, Cerebro-spinal Fever, Erysipelas, Puerperal Fever, Tropical Dysentery, Typhoid Fever, Cholera, Plague.

As all observers are agreed in regard to the personal transmission of the first named of these series (variola, etc.), we need to give attention here only to the other groups; except merely to say that the easily demonstrable existence of a morbid material (virus) in the instances of primary syphilis, gonorrhoea, variola, and vaccinia presents a very cogent analogical argument for the presumption that all clearly contagious (even {137} though non-eruptive) maladies, such as mumps and whooping cough, must also have a morbid material as their essential cause; and also in favor of the supposition that a morbid material may probably be the "causa sine quâ non" of each of the other maladies which are known to be endemic or epidemic. A few theorists only have argued in favor of any other view than this. Sir James Murray and Dr. Craig of Scotland, and Dr. S. Littell of Philadelphia, have sustained an electrical hypothesis, and Oldham and others have advocated one connected with changes of bodily temperature, or ozone, etc., for the origination of certain endemic and epidemic diseases. But all the facts point toward the existence of material causes, specific for each of these disorders, and many observations and much ingenuity of reasoning have been brought to bear upon the question as to their intimate nature.

Are these materiæ morborum merely inorganic elements or compounds entering human bodies and acting there as chemical poisons? Against such a supposition we have, as almost decisive objections, not only the absence, under the most searching analysis, of any chemical peculiarity in the air of malarious or otherwise infected regions, but also the clinging of many endemic and epidemic causes (as known by their effects) to particular localities, notwithstanding the recognized law of the diffusion of gases which must antagonize such concentration. Therefore, we may rule out, as highly improbable at least, the hypothesis of the inorganic gaseous nature of malaria, as well as of the essential causes of yellow fever, cholera, plague, and the other analogous diseases.

By the once general use of the term zymotic, there is suggested a line of thought which has been quite prevalent since the prominence of Liebig's teachings in chemical physiology, until recently. That great chemist did not imagine that a true zymosis or fermentation occurs under the action of a virus upon the human economy. His thought was more clearly expressed, in the phraseology of the late Dr. Snow of London, as the theory of continuous molecular change. Its most striking physical instance or analogue is the extension of flame from a burning body to combustible matter within its reach. Sugar formation from starch by diastase, and the change of albumen into peptone by pepsin, are familiar examples, in organic materials, of the propagation of molecular movement in special directions and with characteristic results. It does not seem to be more than a short step from these to the processes which we study in fermentation, putrefaction, septicæmia, and the multiplication of small-pox contagion, from the smallest inoculation, in the human body.

But here comes in a new hypothetical factor, introduced by the aid of {138} the microscope, although anticipated conjecturally before actual discoveries in this field were made certain. So prominent is this subject in the discussions of the present time, under the expression "the germ theory of disease," that we are justified in giving attention to it here somewhat at length.

Stahl proposed a purely chemical theory of fermentation early in the seventeenth century. Not much later Hauptmann suggested the probable causation of epidemic diseases by minute living organisms. Linnæus revived this hypothesis in the eighteenth century. These two topics of inquiry, with the intermediate one of putrefaction, then received much attention, at first apart, but afterward with recognition of their analogies. When Fabroni, Cagniard de la Tour, Schwann, and Kützing had, with the aid of the microscope, made familiar the life-history of the yeast-fungus (Saccharomyces cerevisiæ), more close consideration still was given to these remarkable changes in organic materials and forms, dead and living.

Starting from the physical basis of inorganic chemistry, Liebig followed the series up from the so-called catalytic action by which the presence of a substance, itself apparently unchanged, induces reaction between two or more other bodies, to those which occur within plants and animals, as examples of vital chemistry. Such is the influence of diastase or invertin, which in the seeds of plants brings on the conversion of starch into sugar and of cane-sugar into glucose and levulose. Such is the agency of ptyalin in the saliva, of pepsin in the gastric juice, and of pancreatin or trypsin in the secretion of the pancreas, in the processes of digestion. From these it appears to be an easy transition to those changes which occur in organic matter no longer living, as in the fermentation of vegetable juices and the putrefaction of animal tissues. Liebig endeavored to explain these also in the same manner as the chemico-vital processes; and he then went farther to apply the same generalization to the propagation of disease, by what is called virus, in the instances of contagious, endemic, and epidemic maladies.

But, meanwhile, observation and speculation gave almost equal prominence to the importance of minute living organisms in the apparent instigation of all these evidently analogous changes of fermentation, putrefaction, suppuration, septicæmia (Piorry, 1835), infection, and contagion.

Upon this side the leading investigator for many years has been Pasteur. As long ago, however, as 1813 Astier, and in 1840 Henle of Berlin, and near the same time Sir Henry Holland of London and Dr. J. K. Mitchell of Philadelphia, gave expression to opinions of a similar kind, based upon many important facts before very much overlooked. By exact experimentation, moreover, Schwann, Helmholtz, Schroeder, and Dusch ascertained that the agent or agents causative of fermentation and putrefaction can be detained by heated tubes, by animal membranes, {139} and by cotton wool, anticipating the later observations of Pasteur, Tyndall, Chauveau, and others to the same or similar effect. These results of experiments are commonly understood to prove the particulate character of the agents so studied. What may be called an era in the practical application of etiological inquiry dates from the introduction by Lister (about 1860) of the principles of antiseptic surgery, based upon the theory that disease-germs, derived from the atmosphere or other external sources, are the essential causes of suppuration, septicæmia, pyæmia, gangrene, etc. following injuries or operations.

So far from this inquiry being yet terminated, while experiments and observations have become more and more numerous and elaborate, opinions continue to differ; and we must yet await the time when, by successively excluding, one after another, all the sources of error, a truly scientific conclusion may be obtained.

Roughly speaking, it may be said that parties in the debate are chiefly ranged upon two sides--those who favor the probability that only chemical, not vital, action is to be traced in fermentation, putrefaction, suppuration, infection, and contagion; and those who regard minute organisms, discovered or undiscovered, as causative of, and indispensable to, all these processes.

Without intention of injustice to other able investigators, the principal names so far associated with the former of these views may be thus mentioned: Panum (1856), Robin, Bergmann, Liebig, Colin, Lebert, Vulpian, Onimus, B. W. Richardson, Beale, Senator, Rosenberger, Hiller, Nægeli, Schottelius, Harley, Jacobi, Curtis, and Satterthwaite. Of those maintaining, in some form and with more or less positiveness, the disease-germ theory, the most conspicuous, especially as observers, have been Tuchs (1848), Royer (1850), Davaine, Branell, Pollender, Pasteur, Tyndall, Lister, Mayrhofer, Ortel, Letzerich, Nassiloff, Hueter, Toussaint, Hansen, Salisbury, Klob, Hallier, Basch, Virchow, Neisser, Eberth, Tommasi Crudeli, Klebs, Talamon, Schüller, Tappeiner, Cohnheim, Koch, Baumgarten, Buchner, Aufrecht, Birch-Hirschfeld, Greenfield, and Ogston. Besides these the elaborate studies of microphytes by Cohn, and those of Coze and Feltz, Waldeyer, Recklinghausen, and others upon septic poisoning, have been of acknowledged importance; and the experimental labors of Burdon Sanderson in England, and Sternberg, H. C. Wood, and Formad in the United States (under the auspices of the National Board of Health), possess great value. But the scientific caution of these last inquirers, like that of Magnin, has prevented them from formulating, as yet, positive and final opinions upon the subject. It is not saying too much to assert nearly the same of {140} several of those mentioned above, as inclining to one or the other side of the controversy.

It would appear, then, that the data for a final conclusion have not yet been made certain. Several hypotheses are conceivable, and capable, each, of plausible support:

1. The purely chemical theory of Liebig, Gerhardt, Bergmann, Snow of London, and B. W. Richardson.

2. The bioplastic hypothesis of Beale, according to which germinal matter may be detached from a living body and planted, while yet retaining vitality, upon another, and there may undergo changes more or less morbid, and destructive of the body by which it has been received. This theory of migrating or transplanted bioplasts has received very little support besides that of its distinguished author.

3. That the minute organisms discovered so constantly upon diseased parts of plants and animals (e.g. ergot of rye, Peronospora infestans of potato-rot, Botrytis Bassiana of silk-worm muscardine, Panhistophyton of silk-worm pebrine, Empusa muscæ of the fly, Achorion, Tricophyton, Oidium, and Leptothrix of human affections of the skin and mucous membranes) are incidental or accidental only--acting, as R. Owen observes, {141} most commonly as natural scavengers in the consumption of effete organic material; but that they may become noxious under two sorts of circumstances--viz. when their numbers are enormously increased, as is known to be the case with trichinæ in the human body, and also when they are brought in considerable number into contact with bodies already diseased, or at least suffering under depression of vital energy.

Against the inoculation and inhalation experiments of Villemin, Tappeiner, Koch, Wilson Fox, and others, by which the specific character of tubercle has been said to be proved, must be placed those of Sanderson, Foulis, Papillon, Lebert, Waldenburg, Schottelius, Wood and Formad, Robinson, and others, by which tubercles have been induced by the injection, inoculation, or inhalation of various non-tubercular materials. In answer to the argument from these, it is asserted by Koch and his supporters that "there is no anatomical or morphological characteristic of tubercle," its only sufficient test being its inoculability. This is almost begging the question; at all events, it leaves it, for the present, unsettled. Moreover, tubercular deposits do not always contain bacilli, as has been shown by Spina, Sternberg, Formad, Prudden (N.Y. Medical Record, April 14 and June 16, 1883). The last named made, in one well marked case, six hundred and ninety-five sections from ninety-nine tubercles in different portions of a tuberculous pleura, all of Koch's precautions being observed in the examination. Belfield (Lectures on Micro-Organisms and Disease) admits the possibility that tuberculosis may be produced by either of several causes. It has, at least, not yet been demonstrated that the tubercular tissue is more than a nidus or favorable "culture-ground" for the bacilli, or that, in the presence of a constitutional predisposition, they may not merely promote a more rapid destruction of the invaded organs or tissues.]

4. That such organisms are the essential and direct causes of enthetic maladies by invading the human and other living bodies as parasites, consuming and disorganizing their tissues, blood corpuscles, etc. Pasteur considers the abstraction of oxygen an important part of their action.

5. That these microbes, microphytes, or mycrozymes act not as parasites, but as poison-producers, secreting a sort of ferment which is the specific morbid material (Virchow); or, when multiplying in excess of their food-material, they may die, and their dead bodies, like other decaying organic matter, may become poisonous. This possibility, although not distinctly suggested (so far as I know) hitherto, appears to me to be not unworthy of consideration. That the numbers of micro-organisms present have some important relation to morbid conditions has long since been inferred from familiar facts.

6. That they are not generators, but carriers, of disease-producing poisons; their vitality giving to the latter a continuance of existence and capacity of accumulation and transportation not otherwise possible.

Briefly, the following is a summary of the most generally accepted classification of those microscopic organisms whose rôle in the causation of diseases is now under discussion; chiefly following Cohn and Klebs:

Orders: Hyphomycetæ, Algæ, Schizomycetæ.

Hyphomycetæ, genera: Achorion, Tricophyton, Oidium.