BACILLUS ANTHRACIS 27 



process becomes more and more hyaline until the 

 spore comes to be free in the original cell envelope, 

 and finally, by the disappearance of this envelope, is 

 set entirely free. The preparation (Fig. 17) which 

 is made from such a culture as that described shows 

 the process of spore formation, which is unequally 

 advanced in the various filaments. The spores are 

 unstained and appear as clear oval spaces in the 

 stained bacilli and are most advanced and best seen 

 in the shorter filaments to the left of the photo- 

 graph. 



Spore formation requires the presence of free 

 oxygen, and occurs at temperatures between 15 C. 

 and 42 C. ; it is most free at about 20 C. to 25 C. 

 The growth of the vegetative cell takes place at 

 temperatures ranging between 12 C. and 45 C. ; the 

 optimum temperature is about 37 C. The vegeta- 

 tive cell is killed at 60 C., and the spore at 120 C., 

 though the mode of applying the heat and the 

 length of time of exposure modify the result. 



To the growth and formation of long intertwisted 

 filaments and chains of bacilli, as described above, are 

 due the characteristic microscopic appearances of 

 anthrax cultures. In bouillon the growth forms 

 cotton-wool-like masses, which remain coherent 

 -even when the culture is shaken. As the growth 



