When bacteria are injected into the animal body, they produce different effects according to the original nature of the bacteria or bacilli, the conditions under which they have been cultivated, and the quantity introduced. There is probably another factor of no less importance, which, however, still requires to be investigated, viz. the condition of the body (p. 97) into which they are introduced. In considering the effect of an injection into the living body of a solution containing bacilli, we must be careful to distinguish between the effect of the bacilli themselves, after their introduction into the circulation, upon the tissues and organs of the body, and the effect of the substances which they have already formed in the solution before their injection.

1 Klein, Quarterly Journ. of Microscopic Science, Jan. 1883.

2 Inaugural Dissertation (Gottingen), 1881.

3 National Board of Health Bulletin, Supplement No. 17, Jan. 21, 1882.

We must distinguish between those two things in the same way as we would have to distinguish between the effects of the particles of the yeast-plant and the effects of the alcohol which it had formed, if we were to inject a solution in which yeast was growing into the veins of an animal. The yeast or the bacteria would have one effect upon the animal, the alcohol or the septic products of the bacteria would have another.

Solutions of putrid organic matter containing numerous bacteria cause high fever and often death.

The course of the fever depends on the specific nature of the bacteria, e.g. septic bacteria, anthrax bacilli, etc.

It is difficult at present to ascertain exactly how far all the following diseases are due to the presence of microbes or their products; but it has been found that micrococci cause erysipelas, acute necrosis, gonorrhoea, gonorrhoeal ophthalmia, contagious ophthalmia, ophthalmia neonatorum, and are present in pyaemia, puerperal fever, ulcerative endocarditis, infective myositis, and contagious pneumonia. When malignant oedema or traumatic gangrene occur, bacilli are usually found. Micrococci are also supposed by some to be the cause of vaccinia and of diphtheritic inflammation. The bacillus anthracis produces anthrax; bacillus septicaemias, blood-poisoning; bacillus malaria?, ague and malarious diseases; bacillus tuberculosis, phthisis; bacillus leprae, leprosy; and another bacillus is the cause of glanders. In relapsing fever the spirochaeta Obermeyeri is found in the blood, and is probably the cause of the disease.