Fig. V. Spores of Bacillus Anthracis. X 1500. 



When the food of this bacillus begins to fail it forms spores which are surrounded by 

 walls thicker than the germ itself was; these enable it to survive seasons of heat or cold or 

 drouth tbat would be fatal to the germ itself. The formation of these spores caused the 

 first virus Pasteur tried to prepare to become more instead of less virulent. The presence 

 of spores with thick walls sometimes prevents boiling from sterilizing a liquid. 







Jr 



'"*%,* 



U 



Fig. VI. Hog Cholera. X 1503. 



(487) 



