VIBRIO CHOLERA. 363 



dal power is heightened, but the animal is not really more 

 resistant to cholera toxin than it was originally. See below 

 concerning R. Pfeiffer's biologic cholera reaction. See 

 also R. Pfeiffer (Z. H. xvi, 258), M. Gruber, and Wiener 

 (A. H. xv, 241). 



One principal difficulty in the animal investigation of 

 cholera is the variable, easily reduced virulence of the 

 cholera vibrio. Many methods are recommended to in- 

 crease the virulence; for example, the anaerobic cultiva- 

 tion in hens' eggs (Hiippe), which is contested by Wes- 

 brook (H. R., 1896, 241), also passage through pigeons 

 (Gamaleia, Salus, etc.). W. Rindfleisch, however, insists 

 that no example of the cholera vibrio can be cultivated 

 which is distinctly pathogenic for pigeons when injected 

 subcutaneously (Z. H. xxi, 247). "Young" cultures, 

 upon which many writers place great value, are only 

 apparently more virulent, because they contain many 

 more living individuals than older ones (Gottschlich and 

 Weigang, Z. H. xx, 376). 



According to Blachstein, the virulence of cholera vibriones is en- 

 tirely dependent upon the nutrient medium. It is said that a cholera 

 culture which is no longer virulent may be rendered virulent by culti- 

 vating it as follows : 



1. Two days in a 2% peptone solution, which contains besides only 

 0.5% disodium phosphate and is cleared up with a little ammonium 

 citrate solution. 



2. Nine days in a 2% peptone solution containing also 3% potas- 

 sium nitrate. 



3. One day upon the solution given in 1, with the addition to each 

 100 c.c. of 1 c.c. of a cold saturated solution of ammonium-ferro- 

 sulphuric acid. 



(b) In man: In a considerable number of cases, follow- 

 ing the example of v. Pettenkofer and Emmerich, previ- 

 ously healthy men, after swallowing small quantities of 

 pure cultures of the cholera vibrio, have developed the 

 symptoms of cholera of slight or medium severity. The 

 persons on whom the experiments were conducted usually 

 had previously taken some soda solution to counteract the 

 acidity of the stomach. Several severe and one fatal case 

 of ' ' laboratory cholera ' ' have been known to occur in 

 men who were working with cholera vibrios. (See Reincke, 

 C. B. xvn, 202.) According to R. Pfeiffer, cholera in 



