Robert Koch Growth Quotations

To prove that tuberculosis is caused by the invasion of bacilli, and that it is a parasitic disease primarily caused by the growth and multiplication of bacilli, it is necessary to isolate the bacilli from the body, to grow them in pure culture until they are freed from every disease product of the animal organism, and, by introducing isolated bacilli into animals, to reproduce the same morbid condition that is known to follow from inoculation with spontaneously developed tuberculous material.

... After it has been determined that the pathogenic organism is present in the animal body, and after it has been shown that the organism can reproduce in the body and be transmitted from one individual to another, the most important experiment remains to be done....to determine the conditions necessary for growth and reproduction of the microorganism.