ASIATIC CHOLERA. 59 



free filtrate and kept in the dark were found to lose only one-third 

 of their toxicity after six months. Guinea-pigs were found to be 

 most susceptible; rabbits somewhat more resistant; mice required 

 relatively twenty times the dose fatal to guinea-pigs ; while pigeons 

 and chickens were still less susceptible. By gradually increased 

 doses, guinea-pigs, rabbits, goats, and horses were immunized with 

 this toxin. From a guinea-pig thus immunized an antitoxic serum 

 was obtained, and it was found that one c.c. of this was sufficient to 

 neutralize four c.c. of a toxin, two-thirds c.c. of which sufficed to kill 

 a guinea-pig of 250 grams in 14 hours. By treating a horse for 

 six months with gradually increased doses of the toxin these investi- 

 gators secured an antitoxic serum, 1 c.c. of which was sufficient to 

 neutralize four times the fatal dose of the toxin. The antitoxic 

 serum was also found to give immunity against intra-peritoneal in- 

 fection with living cultures. From these experiments it was con- 

 cluded that in the treatment of cholera an antitoxic, and not an 

 anti-bacterial, serum is needed. It should be stated that a highly 

 active toxin is necessary for the production of a useful serum. 



It is more than probable that the cholera toxin is formed within 

 the cell by synthetical processes, and that it readily diflfuses through 

 the cell wall. On this assumption both Pfeiffer and MetschnikoflF 

 are partially right in their contentions. 



Bujwid found that on the addition of from 5 to 10 per cent, hydro- 

 chloric acid to bouillon cultures of the cholera bacillus there is de- 

 veloped after a few minutes a rose-violet coloration, which increases 

 during the next half hour and in a bright light shows a brownish 

 shade. The coloration is more marked if the culture be kept at about 

 37°. In a pure culture this reaction does not occur.* 



Brieger found that this color is due to an indol derivative. In 

 cholera cultures on albumins he obtained indol by distillation with 

 acetic acid. 



Dunham finds the best medium for the " cholera reaction " to be 

 a one per cent, alkaline pepton solution, with one-half per cent, of 

 common salt. Bujwid prefers a two per cent., strongly alkaline, 

 pepton solution with salt. Jadassohn finds that gelatin cultures give 

 the reaction both before and after the liquefaction of the gelatin. 

 The undissolved gelatin, after the addition of hydrochloric or sul- 

 phuric acid, becomes rose-violet. Cohen claims that cultures of 

 other bacilli give a similar coloration, but Bujwid explains that the 

 results obtained by Cohen were due to the use of impure acids, 

 which contained nitrous acid. Salkowski agrees with Bujwid, and 

 states that when acids wholly free from nitrous acid are used the 

 reaction is characteristic of the comma bacillus. He explains the 



•Poehl deserves the credit of being the first to call attention to this reaction, 

 though his work was evidently unknown to Bujwid at the time when the latter pub- 

 lished his report. 



