8 The Microscope. 



the discovery of the cause of infectious diseases. He is satisfied 

 that wliat he has done for tuberculosis and cholera, and what 

 others have accomplished for other maladies that are less deadly, 

 such as erysipelas, could also be done for all diseases, whatever 

 they may be. From this it may be seen that his labor on be- 

 half of science is not yet finished. It appears in fact that Koch 

 has for the time being abandoned the examination of microbes. 

 for a study of their destruction in the living human body. 



Fig. 2. — The same bacilli examined under the 

 microscope after fourteen days' development. 



Prof Koch; first;; commenced experiments with a tube here 

 represented. It is an ordinary test tube, such as is used in all 

 ordinary experiments. It is, in the first place, sterilized over 

 the fire, then a bouilon of sterilized culture is poured into it, 

 that is to say, culture which does not contain any germ. This 

 bouillon is prepared with agar-agar, a sort of gelatine. When 

 this had been done the microbe, which is taken directly from the 

 mucus of a consumptive, is placed in the tube and the orifice 

 closed with cotton, thereby permitting the air to pass into the 

 the vessel, but retaining the organisms which are held suspend- 

 ed therein. The tube thus prepared is subjected to an even 

 temperature in an oven. After a certain length of time the 

 microbes begin to develoji and increase, and assume the clotted 

 appearance which we seein Fig. 8 of the engravings. But in 



