606 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



ant spore state did form in liquids it would be present. It is highly probable, how- 

 ever, that if cultures but a few days old had been chosen the bacteria would have 

 resisted drying much longer. These experiments give the following results: 



A liquid'culture eleven days old resisted drying for nine days; another, ten days 

 old, at least teii days. Bacteria in tissue may resist destruction after drying for from 

 twentv-two to forty-nine days. 



The'method of drying the bacteria on cover-glasses and introducing the latter into 

 liquid does not inform us wliether most bacteria die within the same time or whether 

 some resist much longer than others. Hence the following expedient was resorted 

 to, which Koch had introduced in the study of disinfectants: Silk threads sterilized 

 by boiling several times in distilled water were dried and steeped in a beef infusion 

 peptone culture about one week old. The culture containing the threads was al- 

 lowed to dry in the incubator for one day, then placed in a sterilized bottle plugged 

 with cotton. Each day, beginning with the second, one or two threads were placed 

 in a layer of nutritive gelatine on a glass plate so that the thread was completely 

 covered by the gelatine. Characteristic colonies of the bacterium appeared around 

 tlie thread within two days, though the plates were usually kept under observation 

 five days. For twenty-one days isolated colonies and groups of colonies appeared 

 in moderate abundance on the threads, when the stock of the latter was exlmusted. 



In another similar series the threads were laid upon a sterile plate and a twenty- 

 four hours' liquid culture poured upon them and allowed to dry uncovered in the 

 incubator for one day. These threads, still undisturbed on the plate, were placed 

 in the laboratory, covered with a bell glass. On the fifteenth day the testing began, 

 a single thread being placed in the gelatine layer each day for sixteen days. Col- 

 onies of the bacterium developed in large numbers until the twenty-second day, 

 when they diminished in number. On the twenty-seventh and twenty -eighth days 

 no colonies appeared. On the three following days a few appeared, when the series 

 was closed. 



The bacterium of hog-cholera may therefore remain alive, during 

 continuous desiccation, for from ten days to nearly two months. The 

 variation in the results obtained is no doubt due to the different vi- 

 tality of the cultures used. The gelatine-plate method is not so deli- 

 cate a test as the method of liquid cultures, as it would be diflEicult 

 to tell when the last bacterium died, a single colony under the thread 

 escaping observation very easily. A single bacterium would invari- 

 ably reveal its presence in a liquid after a time by multiplication. For 

 the same reason the latter method needs greater care; the liquid cult- 

 ures must be examined microscopically, and if there be any doubt 

 still remaining they must be tested on gelatine; for a single foreign 

 microbe gaining access to the culture tube might introduce an error 

 into the results, which is easily avoided on the gelatine plate by ob- 

 serving the characters of the colonies. 



It had been determined by a large number of experiments that 

 cultures of the bacterium of hog-cholera can be sterilized — in other 

 words, that the bacterium itself may be destroyed — by an exposure to 

 58° C. for from 15 to 20 minutes. To determine whether dried blood 

 or spleen tissue containing the bacterium was more resistant the f ol- 

 lowmg experiment was tried : 



Spleen pulp from a case of hog-cholera was rubbed upon sterile cover-glasses 

 and allowed to dry under a plugged funnel for 24 hours at a temperature of 65° to 

 75° F. Four tubes of beef infusion, after a cover-glass had been dropped into each, 

 were exposed to a temperature of 58" C. for 15, 20, 29, and 41 minutes, respectively. 

 These remained ]>ermanently sterile, while a fiftli tube, which had been inoculated 

 in the same way but not heated, contained on the following day a pure culture of the 

 hog-cholera bacterium. It should be added that each cover-glass contained a con- 

 siderable number of germs, according to microscopic examination of different parts 

 of the spleen. 



The bacterium within the body of the diseased animal cannot there- 

 fore be regarded more resistant than when cultivated in liquids. 



Effect of boiling water. — Culture tubes containing about 10'"'^ of meat infusion 

 were placed in boiling water until at the boiling-point. They were then removed, 



