INDOL FORMATION. 345 



tion 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 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, mistained 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 representatiou of retraction of protoplasm, with producUoa of 

 pale points, in bacillus typhi abdominalis. 



Owing to a tendency to retraction of its protoplasm 

 from the cell envelope and the consequent produc- 



' See A. W. Peckham : The Influence of Environment npen the Biological 

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

 vol. ii. 1897. 



