(2) The microbes shall be isolated from these and cultivated in suitable media until obtained in pure culture. That is to say, matter containing the microbe, taken from the infected source, must be cultivated in artificial media outside the animal body, under conditions excluding the possibility of the introduction of other microbes, until pure cultures of these microbes are obtained, and these microbes must be transplanted from generation to generation, until it is certain that no trace of non-living matter derived from the original animal body remains in the culture. (3) A pure culture of the microbe, thus obtained, shall, when introduced into the body of a healthy susceptible animal, reproduce the disease in question. (4) The microbe in question shall be found in the animal so affected. Kanthack adds a further condition, that (5) The toxins and poisonous substances obtained from the artificial cultivations shall agree chemically and physiologically with those obtained from the diseased animal. All the preceding conditions have been fulfilled for anthrax, diphtheria, and tetanus; and the first four conditions have been fulfilled in regard to tuberculosis, glanders, gonorrhœa, malignant œdema, and actinomycosis. In enteric fever and influenza the first two conditions have been met; but inoculation experiments (3) have failed. In leprosy and relapsing fever the first condition is met, but (2) has failed. In the following diseases the specific microbe has not been isolated, though from analogy it is believed that each of them is caused by such a microbe:— Measles. Rubella (German measles). Typhus fever. Scarlet fever. Varicella (chicken pox). Variola (small-pox). Whooping Cough. Mumps. Hydrophobia, etc. Erysipelas occupies a special position. It is a specific disease due to a microbe, which, when it attacks other parts than the skin, may produce abscesses, boils, or blood-poisoning.