210 BACTERIA. 



destruction of the tissue cells takes place so rapidly, in con- 

 sequence of the invasion of each cell by a large number 

 of bacilli, that nucleus and protoplasm break down com- 

 pletely and the little group of bacilli is set free, or at any 

 rate is not embedded in a mass of protoplasm, but is merely 

 mixed up with the granular debris of the cell, from which, 



Micro-photograph of Tubercle bacilli, found in the scraping from the lung 

 of a cow suffering from Perlsucht. x 1000. 



or along with which, it may be carried to other parts of the 

 body. 



Having found the tubercle bacillus almost invariably accom- 

 panying tuberculous disease, Koch, to complete his proof, 

 wished to separate the organism in the form of what is 

 called a pure cultivation, in order that he might study 

 its life-history, and that he might determine whether 

 the organism when introduced alone into the animal body, 



