EXPERIMENT STATION BULLETINS. 



467 



SO small that they cannot be seen with the naked eye, others may not 

 develop at all in gelatin, while they may do so in milk. But the in- 

 fluence which this possible error will have on the results, does not affect 

 the conclusions. If there are in old milk really more bacteria than we 

 have counted, then the same amount of lactic acid would have been 

 produced by a larger average number, that means the fermenting capac- 

 ity of a single cell would be still smaller than recorded. The decrease 

 of the fermenting capacity cannot be doubted, but perhaps the degree 

 of the decrea>se may. 



♦After 36.5 hours. 

 t.\fter 60 hours. 



This slow growth in gelatin and the small size of the colonies com- 

 pared with those from young, fresh cultures is remarkable, if we con- 

 sider the number of generations necessary to build up a colony. When 

 the old culture A was transferred to the fresh sterile milk, the bacteria 

 had the very best chance for multiplication. But they did not multi- 

 ply readily. Then they were transferred to lactose gelatin, but even 

 there the colonies developed slowly. In sample E^ for instance, there 

 were 12,900 cells in the beginning and 80,000,000 after 24 hours. This 

 means eleven or twelve generations under the vei^r best conditions of 



