1898.J MICROSCOPICAL JOURNAL. 139 



It is customary, therefore, to add to the media certain 

 substances that are known to retard the multiplication of 

 the rabble, whilst they favor the growth of the few. 

 The addition of l-500th per cent of carbolic acid acts in- 

 this way, and is largely used in the case whore, e. g., it 

 is required to find bacillus colt. By adding sewage to 

 phenolated broth a pure culture of B. coli may be 

 obtained. This medium is favorable also to the typhoid 

 bacillus, and both multiply well in a medium prepared 

 from a sterilized infusion of potato mixed with gelatin 

 and iodine. The incubation period for these two varie- 

 ties of bacillus varies from twenty-two to forty-eight 

 hours. It was noticed that whereas the B. coli develops 

 carbon dioxide the typhoid bacillus does not. The 

 cholera vibrio grows and multiplies best in a medium 

 containing 1 per cent of salt and 1 per cent of peptone. 

 By such devices the specific bacteria may be isolated 

 from other varieties, and in the form of a sub-culture 

 spread upon glass, dried, stained, and examined. In 

 1893 the value of this selective method was proved in a 

 striking manner. A man died from an unknown cause, 

 an inquest was held on tlie body, and as a result the 

 death attributed to pnuemonia. Another doctor, some- 

 what sceptical about this conclusion, took a portion of 

 the dead man's bowels, mixed it with gelatin and placed 

 it in an incubator for ten days. Then a portion of the 

 putrid, evil-smelling substance was transferred to a pep- 

 tone solution, a plate culture of the same prepared, and 

 the presence of the cholera bacillus proved beyond the 

 shadow of a doubt. Dr. Klein described another method 

 of sifting, depending on the principle that whilst some 

 bacteria thrive in air, others are killed thereby. These 

 two classes are described respectively as JBrobic and 

 anaerobic bacteria. The cholera bacillus and B. coli are 

 examples of the former class. Aujerobic conditions are 

 attained by a variety of methods, including the absorp- 



