204 



STUDIES ON FERMENTATION. 



It seems, therefore, impossible to admit that caseous ferment 

 results from a modification of " high " ferment, and we are 

 led to believe that in the preceding experiments it must have 

 been the progeny of cells of caseous ferment present in the 

 " high " yeasts of commerce, which cells, probably in con- 

 sequence of their scarcity, the microscope was unable to reveal, 

 but which, nevertheless, did exist, and went on reproducing 

 themselves alone after the heating. 



This conclusion is supported by the following fact, which also 

 tends to prove that in the case of the " high " English pale aks, 

 caseous ferment plays a most important part. In the medium 

 already described, we sowed the deposit from a bottle of good 

 English pale ale. After having been heated the yeast went 

 on growing, and we obtained the very beautiful specimen of 

 caseous ferment represented in Fig. 47. The two dark globules 



Fig. 47. 



are dead cells which had been killed. Two minute segments 

 of lactic ferment are also visible in the sketch — the yeast 

 which we sowed was, of course, impure — and their presence 



sequence of the tenderness of its tissues. At the end of a fermentation, 

 and even several months afterwards, it might be safely heated to 50 C. 

 (122° Fahr.) without anj' harm to it. " Low " yeast also can withstand a 

 temperature of 50" C. in the medium in question. 



