INDOL FORMATION. 345 



tion 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 become red. In the fermen- 

 tation-tube, in glucose or lactose bouillon, no evolution 

 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. 



FIG. 70. 



Diagrammatic representation of retraction of protoplasm, with production of 

 pale points, in bacillus typhi abdominalis. 



Owing to a tendency to retraction of its protoplasm 

 from the cell envelope and the consequent produc- 



1 See A. W. Peckham : The Influence of Environment upon the Biological 

 Functions of the Colon Group of Bacilli. Journal of Experimental Medicine, 

 vol. ii. 1897. 



