﻿IX. B. 1 Barber: Carriers of Asiatic Cholera 3 



deposited in places where they can readily dry, but when dis- 

 charged on moist food vibrios may remain for some time. To 

 test this matter, some fresh cockroach faeces were placed on four 

 different kinds of food : fresh beef, lettuce, fish, and clams. In 

 every case, the cholera vibrios remained viable for at least sixteen 

 hours at room temperature. 



In this connection it may be worth while to mention the results 

 obtained by me in some recent experiments on the longevity of 

 cholera vibrios in human faeces placed on various foods in use 

 in this locality. Here, as in the case of the experiments with 

 cockroach faeces, the cholera vibrios must compete with the other 

 bacteria present in the faeces and with the microorganisms 

 already present in the food. On the cut surfaces of a cucumber, 

 a chico, and a papaya fruit — all distinctly acid to litmus — and 

 on the leaves of lettuce, the cholera vibrios survived overnight 

 in one experiment. In another test, cholera vibrios in human 

 faeces survived twenty hours on the cut surfaces of cucumber 

 and papaya fruits, but failed to live forty-four hours. On" 

 two varieties of shrimp, cholera vibrios in human faeces re- 

 mained viable twenty-two hours; on oysters, forty-six hours; 

 and on the inside of an opened clam, four days. In all of these 

 four foods, other bacteria were very numerous; in the oysters, 

 especially, they were so plentiful that the food was acid in reac- 

 tion when the cholera vibrios were placed on it. It is probably 

 fair to assume that cholera vibrios, when abundant in cockroach 

 faeces, would survive as long on foods as when in human faeces. 



In addition to their faeces, the vomit of these insects may also 

 be a source of danger. A faeces-fed cockroach was observed to 

 disgorge portions of its meal at intervals of ten minutes, twenty 

 minutes, and sixty minutes after feeding — sufficient time to allow 

 the insects to travel from a closet to human food. The sixty- 

 minute sample contained many cholera vibrios. These insects 

 often discharge a thin saliva from the mouth. This fluid seems 

 to be nearly, if not quite, bacteria-free, and tests failed to show 

 any cholera vibrios in it. The vomit mentioned above is of a 

 different nature, as shown by the carmine tint and by bacteria 

 and other substances seen in microscopical examination. 



As might be expected, cockroaches show no evidence of infec- 

 tion by cholera. The vibrios are simply held in the intestine, 

 and apparently become no more numerous than in the ingested 

 human faeces. In order to determine if there is any loss of viru- 

 lence in cultures of cholera vibrios isolated from cockroach 

 faeces, a comparative test was made by guinea-pig inoculations. 



