The FermentaHon Tube 225 



less neutral and therefore favorable to their continued multi- 

 plication. A good illustration of this fact is afforded by the 

 growth of B. coli in saccharose bouillon. The gas production 

 goes on (with most varieties) very slowly. The fluid in the 

 bulb in contact with the air becomes alkaline and very turbid 

 with growth. The fluid in the closed branch becomes acid 

 under the influence of the slow fermentation and remains so. 

 As it is gradually pushed out into the bulb by the slow accu- 

 mulation of gas it tends to reduce, by degrees, the alkalinity 

 of the fluid therein contained and thus favors step by step, the 

 growth which finally becomes very dense. 



The emploj-ment of sugar as a constituent of culture media 

 is therefore, a matter of considerable importance. For certain 

 species, like D. coli for instance, the addition of i per cent, 

 glucose or lactose would be a decided detriment to the culture 

 and soon lead to its destruction. Cane sugar on the other 

 hand, added in the same proportion, would favor the growth 

 owing to its much slower decomposition. Again the addition 

 of very small quantities of glucose from time to time is favor- 

 able as stated above. In fact, bouillon, entirely free from 

 muscle glucose, is less desirable than that containing traces, 

 and in general it would be well to add glucose to bouillon. 

 The limit may safely be put at o.i per cent. These remarks 

 apply equally well to the large group of bacteria which pro- 

 duce acids in sugar solutions without the evolution of gas and 

 in searching for the most favorable media for any species its 

 behavior toward the more common carbo hydrates should be 

 carefully looked into. 



APPLICATION OF THE FERMENTATION TUBE TO PROBLEMS 

 IN PRACTICAL SANITATION. THE GAS TEST IN THE DIF- 

 FERENTIATION OF B. TYPHOSUS FROM THE B. COLI GROUP 

 OF BACTERIA. 



The use of the fermentation tube as an important differen- 

 tial test in bacteriology led me in 1889 to compare the fre- 

 quently confounded species, B. typhosus and B. coli communis. 

 A sharp distinction was at once detected between them which 

 manifested itself by a total lack of gas production on the part 



