The germ theory of disease, therefore, may be said to have commenced with the discovery of bacteria in the • blood of diseased animals and men. What are these bacteria? They are small microscopic homes having various forms, sometimes existing in innumerable quantities in putrescent fluids, especially blood and urine, and often found, both before and after death, in vast numbers in the blood of living animals having certain diseases. They are also found in limited numbers in the blood of animals apparently in health. They vary in size as well as in form, some requiring the highest powers of the microscope for their recognition. They have been classified under differ ent names, the classifications.of Cohn and Billroth being the best known. The outlines of Cohn's classification are as follows: They beloug to the family pliycochromaasa, in the natural order StrizosronEk He divides them into four groups, and also into six genera, whose relations are exhibited in the following table: Group I. Sphaaro•bacteri.... Genus 1. Micrococcus.
Group II. Micro-bacteria Genus 2. Bacterium.
Group III. Desmo-bacteria j Genus 3. Bacillus.
( Genus 4. Vibrio. • Group IV. Spiro•bacteria j Genus 5. Spirillum.
Genus 6. Spirochteta.
Of these genera the bacterium, vibrio, spirillum, and spirochmta were contained in the vibriona family of Ehrenberg. Cohn regards the ferment of contagion to be due to the presence of a variety of spluero-bacteria, the micrococci of Haler. The whole group splitero-bacteria is divided into three Sub-groups, viz. : 1. Chromogen; 2. Zymogen ; and 3. Pathogen, which arc, respectively, the micrococci of pigmentation, of fermenta tion, and of contagion. These organisms are too small to be susceptible of measure ment. Among the pathogen micrococci are the M. paccina, which have•been described by Chauveau and Sanderson as present in vaccine lymph: the M. diphtheriticus, and the M. septicus, found in the miliary eruption of typhus fever, pymmia, and other diseases. The true bacteria, as they are sometimes distinguished, or the bacteria of putrefaction, are divided into two species, the bacterium ter711,0, and the bacterium lincola. The B. termo is a small, dumb-bell shaped body, from whly of an in. in length, having a slow, vacillating motion. The B. linolea is larger and more active. It is rod-shaped. and is the ferment found in sour milk. The desmo•bacteria differ from the true bacteria by united in chains. The group is divided into bacillus and ribria. bacilli are divided into three species, viz.: 1 Bacillus subtilis (the vibrio-snbtilis of Eh•enberg), a thread-like form, found in stale milk—length about of an inch. 2. Bacillus anthracis (the bacterium carthincolare of some writers), which is described by Davaine as an immovable, oblong, highly refractive body, found in the blood of animals affected with anthrax, varying from to and even of an inch,in length. and occasionally found in chains of two or three links. The vibrios are distinguished from all the preceding genera by their rotary motion. (It is convenient to state here that the word bacterium is a slight change of the Greek Bannipzoy, a small staff, rod, or cane. The Latin word for the same is bacillus, whence the use of words to denote these rod-like organisms.) It is claimed that within the last two years the experi ments of Koch, Pasteur and others have demonstrated that various specific diseases are caused by different species of bacteria. The swine-plague is one of these, and the report
of Dr. J. H. Detmers, of Chicago, to the commissioner of agricnitnre, is an inter• estina document, presenting many cogent arguments in favor of the vegetable germ theory of disease, but it is probable that the time has not yet arrived to accept, as final, the conclusions to which, with others, he has arrived. The result of some of his experi ments showed " that an inoculation with bacilli Aud bacillus germs. cultivated in so innocent a fluid as milk, will produce the disease with just as much certainty as an inoculation with pulmonal exudation from a diseased or dead hog; second, that an animal that has been afflicted with the plague has not lost its susceptibility, but may contract the disease again, though probably in a milder form." It appears, from the experiments of Dr. Detmers, which have been confirmed by Dr. Law, of Cornell uni versity, that the special contagion of swine-plague may be communicated to other animals. Dr. Detmers inocculated two heifers with fluids containing the bacilli of swine-plague, and produced the characteristic symptoms and post-mortem appearances of the disease; and he states that he regards the results of his experiments as sustaining the opinion, "that although cattle are not as susceptible to the plague as swine, it may be transmitted to them in a. mild form by inoculation." He remarks that the plague bacteria are not always found. iu great abundance in the blood, because they lodge in the congested parts, blocking up the capillaries and smaller blood-vessels, producing emboli and ulcerous tumors. •In such places the organisms are found in numbers, and also in the lymphatic glands and kidneys. They are also discharged by the intes tines, the lungs, and the skin. He found that the plague was communicated from herd to herd by the contamination afforded by running streaualets in which the bacteria were held in suspension, derived from excrements, or from the carcasses of dead animals had died of the disease. Speaking of measures of prevention Dr. Detmers remarks: "No authenticated case of a spontaneous development of swiue-plague has yet come to my knowledge, and the disease, I am more convinced than ever, can be stamped out, but only by adopting the most stringent measures." The experiments of Dr. Law demonstrate the fact that the swine plague may be _transferred to sheep and rats, and then transferred back to the hog In an intensified form. Virus was taken from a pig which had been infected from that of a sheep, and a second pig was successfully inoculated, the post-mortem appearances and microscopic examinations furnishing the usual evidence of the presence of the disease. Several successful experiments of the sane kind were made. These experiments were followed by inoculations of rats which were infected with all the symptoms of the plague. Virus taken from these rats was employed in successfully infecting pigs in return. Dr. Law is now engaged in a of experiments to determine whether mild inoculations may mit produce a mitigated form which may procure immunity from a second attack. (See SWINE PLAGUE).