432 BACTERIOLOGY. 



2 hours after the injection. In a few hours the animal be- 

 comes sick, the temperature drops gradually to 30 and 

 death eventually results. 



In the case of water which contains but a very few cholera vib- 

 rios, instead of adding a small amount to the Dunham's solution, it 

 is better to add the necessary amount of pepton and salt to 300 c.c. or 

 more of the water, thus converting the suspected water into Dunham's 

 solution. These constituents can best be introduced by adding the 

 calculated amount of a sterile solution containing 20 per cent of pep- 

 ton and 10 per cent, of NaCl, i. e., 5 c.c. per 100 c.c. of water. It 

 should then be placed in a large flask, so as to have as large a surface 

 as possible, and allowed to develop at 37. The subsequent examina- 

 tions are the same as those outlined above. 



It must not be expected that the cholera vibrio which 

 has been isolated will agree in every respect with the class- 

 ical description of this organism. On the contrary, varieties 

 must be expected inasmuch as pleomorphism is more marked 

 in the case of the cholera germ than in any other known 

 species. Usually it is a short, thick, bent rod, but it is pos- 

 sible to have long-, slender, almost straight varieties. Usu- 

 ally it possesses but one whip, but some have been shown 

 to possess as many as four flagella. Moreover, although it is 

 usually exceedingly motile, varieties may be found that are 

 motionless. Some varieties will coagulate milk, others will 

 not. Again, as a rule, the liquefaction of gelatin is slow, 

 whereas some liquefy this medium very rapidly. The indol 

 reaction and virulence, which are especially relied upon in 

 an identification,' are likewise subject to extreme variation. 

 Pfeiffer's phenomenon is described in Chapter XIV. It 

 affords as good a means of differentiation as any known 

 procedure. 



The cholera vibrio may retain its vitality 'in water for 

 a considerable period. It has been kept in sterile tap-water 

 for more than a year. It dies out rapidly in water which is 

 kept at or near the freezing-point. Certain varieties, how- 

 ever, can resist actual freezing for many days. As a rule,. 



