BACILLUS TYPHOSUS. 429 



ized beef-muscle, that the indol-producing function 

 may be induced in the genuine typhoid bacillus obtained 

 directly from the spleens of typhoid cadavers. 1 



It does not produce gaseous fermentation. On lactose- 

 litmus-agar-agar it grows as pale-blue colonies, causing 

 no reddening of the surrounding medium ; though if 

 glucose be substituted for lactose, both the colonies and 

 the surrounding medium may become red. In the fer- 

 mentation-tube, in glucose or lactose bouillon, no evo- 

 lution of gas as a result of fermentation occurs. 



It does not form spores. The irregularities of stain- 

 ing so commonly seen in this organism have in some 

 instances led to the belief that the pale, unstained por- 

 tions of the bacilli indicate the presence of spores. 

 More reliable tests, however, have demonstrated the 

 error of this opinion. (What is the most trustworthy 

 test of spore-formation ?) 



It grows at any temperature between 20 and 38 C., 

 though more favorably at the latter point. It is 

 very sensitive to high temperatures, being killed by 

 an exposure of ten minutes to 60 C., and in a much 

 shorter time to slightly higher temperatures. 



It does not liquefy gelatin. 



It grows both with and without oxygen. 



It does not grow rapidly. 



Owing to a tendency to retraction of its protoplasm 

 from the cell-envelope and the consequent production 

 of vacuoles in the bacilli, the staining of this organism 

 is frequently more or less irregular. At some points in 

 a single cell marked differences in the intensity of the 



1 A. W. Peckham : "The Influence of Environment Upon the 

 Biological Functions of the Colon Group of Bacilli," Journal of Experi- 

 mental Medicine, 1897, vol. ii. 



