BACILLUS TYPHOSUS. 411 



ized beef-muscle, that the indol-producing function 

 may be induced in the genuine typhoid bacillus obtained 

 directly from the spleens of typhoid cadavers.' 



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. 11. 



