The development of infectious and contagious diseases necessitates a certain predisposition, or, as medical science calls it, "disease diathesis." This predisposition to infection and contagion consists in the primary causes of disease, which we have designated as lowered vitality, abnormal composition of blood and lymph, and the accumulation of waste, morbid matter and poisons in the system. Bacteria: Secondary, Not Primary, Manifestations of Disease In a previous chapter we learned how lowered vitality weakens the resistance of the system to the attacks and inroads of disease germs and poisons. The growth and multiplication of microorganisms depend furthermore upon a congenial, morbid soil. Just as the ordinary yeast germ multiplies in a sugar solution only, so the various microorganisms of disease thrive and multiply to the danger point only in their own peculiar and congenial kind of morbid matter. Thus, the typhoid fever bacillus thrives in a certain kind of effete matter which accumulates in the intestines; the pneumonia bacilli flourish best in the catarrhal secretions of the lungs, and meningitis bacilli in the diseased meninges of the brain and spinal cord. Dr. Pettenkofer, a celebrated physician and professor of the University of Vienna, also arrived at the conclusion that bacteria, by themselves, cannot create disease, and for years he defended his opinion from the lecture platform and in his writings against the practically solid phalanx of the medical profession. One day he backed his theory by a practical test. While instructing his class in the bacteriological laboratory of the university, he picked up a glass which contained millions of live cholera germs and swallowed its contents before the eyes of the students. The seemingly dangerous experiment was followed only by a slight nausea. Lately I have heard repeatedly of persons in this country who subjected themselves in similar manner to infection, inoculation and contagion with the most virulent kinds of bacteria and disease taints without developing the corresponding diseases. A few years ago Dr. Rodermund, a physician in the State of Wisconsin, created a sensation all over this country when he smeared his body with the exudate of smallpox sores in order to demonstrate to his medical colleagues that a healthy body could not be infected with the disease. He was arrested and quarantined in jail, but not before he had come in contact with many people. Neither he nor anyone else exposed by him developed smallpox.