GERM THEORY OF DISEASE. A precise definition of the term germ theory of disease is difficult, but in general there are three theories, viz.: the vegetable germ the ory, the bioplasmic germ theory, and the physico-chemical theory. The vegetable germ theory, however, is the one usually referred to when no distinction is made. This theory holds that the vegetable organisms of fungoid and algoid forms are the active agents in producing disease by multiplying within the animal organism, and that the vegetable organisms are the descendants of previous organisms; consequently this theory is distinct from that which holds that the organisms are produced by spontaneous generation. This latter theory is, in reality, the physico-chemical theory. The vege table germ theorists, therefore, believe that all diseases which can be shown to proceed from the introduction of vegetable organisms (and they claim that these are numerous) are epizootic. The bioplasmic theory has its chief advocate in Dr. Lionel S. Beale, who is probably the most accomplished living microscopist. His theory, which has many believers among scientific men, may be briefly stated as follows: Under certain circum stances which may not be perfectly understood, but which nevertheless can be shown to exist, and whose results can be demonstrated, there takes place an abnormal devel opment of bioplasmic particles in the tissues and in the fluids, as from certain injuries, or inflammations resulting from exposure, or pathological states resulting from starva tion or other agencies. A degradation of the bioplasmic particles or of the living mat ter, as bioplasm is called, takes place, and an abnormal organism is formed which has the power of growing and multiplying in suitable pabulum, such as the fluids or tissues of the animal system into which it may be introduced. There are many physicians who do not, however, accept either of these doctrines exclusively, believing that there is evidence that some diseases are produced by vegetable germs, or at least that the principal lesions in some diseases are produced by the multiplication of such germs in quantities which interfere with the circulation, and perhaps thus produce pathological conditions sufficient to account for the other symptoms of the disease. They also believe that the biop]asmic theory accounts for many contagious specific diseases, while iu some cases both causes may operate together, or, at least, in the same body. and, moreover, that putrescent fluids containing no discoverable organisms, except perhaps granular bodies, have the power of producing morbid lesions, although perhaps not of so specific a character as that which obtains in some diseases; hut this is a matter which is by no means settled. The belief in the power of a septic poison from any. thing more than a chemical organization, constitutes what may be called the purely chemical theory of disease, and, of course, has no relation to germs whatever.
Extended and laborious investigations have been made for many years, and much valuable knowledge has been acquired; but, as intimated above, much more knowledge, particularly of the natural history of the organisms which are held to be the cause of disease, and of the circumstances attending their development, as well as those by which the diseases are ushered in, is needed; yet, notwithstanding the deficiencies that may exist, it may he assumed as proved that the action of organized particles, or germs, is the cause of a sufficient number of pathological conditions to justify the assertion that the term germ theory of disease is well founded. The various opinions as to the
particular manner in which the germs act, or whence they are derived, do not alter the question as to the propriety of the title; and it would be difficult to conduct any length ened discussion in pathology or medical practice without assuming that living germs are propagators of disease, so widely is the theory accepted. The doctrine may be said to date back at least two centuries, but till recently it was supported by little more than hypotheses, as it was not possible until' a considerable degree of perfection had been attained in the construction of the microscope, and until repeated experiments of vari ous kinds had taught great caution as to this explanation, that a sufficient number of scientific facts could be collected to famish a basis for demonstration of a theory. In 1839, sir Henry Holland advocated an animalcular theory, and in 1847, Dr. J. K. Mitchell of Philadelphia published a volume in which he advocated the doctrine that malarial and epidemic fevers are produced by the introduction into the system of crypt °gamic organisms. Before Linmeus, the great Swedish botanist, broached a aimilar hypothesis. The germ theory of disease, •owever, as a theory, began to be developed between 1840 and 1850. About the latter date, MM. Payer and Davaine of France discovered microscopic bodies in the blood of animals affected with anthrax, which they described as being about twice the length of a red blood-globule. After; wards, in 1857, Brauell found multitudes of rod-like bodies in the blood of men, horses, and sheep dying of anthrax, and he Also found them in the blood of diseased animals, front one to ten days before death. But he did not find them in the blood of convales cent animals, which circumstances caused him to regard these organisms as yielding valuable diagnostic and prognostic Information; but he also came to the conclusion that they did not themselves constitute the poison df anthrax, and that they were not even the carriers of it, because he infected animals with blood which, as he said, did not contain them. Davaine, in 1863, pronounced the rod-like bodies to be bacteria, and afterwards called them bacteridia, to distinguish them from the bacteria of putrefaction. Ile showed that bacteridia were always present in anthrax. According to prof. Otto Bollinger of Munich (Ziemssen's Cyclopadia of lliedicine),.anthrax .organisms are found on sods containing much decaying vegetation, as peat moors, dried-up ponds and freshly turned up soils, where intermittent fever prevails; such sections have been termed anthrax districts; but he also says that in many of these there is no intermittent fever; and also that this disease often prevails where. there is no anthrax. Bollinger, however, remarks that although the microscope may show that no rod-like bacteria may be present in infectious blood of diseased animals, he has always found the germs present in the form of spherical bacteria.