on Milk and Milk-Products. 
381 
the bacillus causing lactic fermentation contains a chemical 
ferment. So far, however, all efforts to isolate the latter have 
failed, and with our present knowledge Ave are unable to say 
whether or not the hydration, like the more noticeable decom- 
position, is purely a physiological action of the micro-organisms. 
It appears that lactic fermentation cannot proceed except in 
the presence of free oxygen, although very small quantities of 
the latter are sufficient to produce in milk as much acid as is 
necessary to coagulate the casein. The presence of a certain 
quantity of acid interferes with the further action of the 
ferment. Less than one per cent, seems to be the maximum 
quantity of lactic acid which can be produced in any solution. 
The complete conversion of a given quantity of sugar into lactic 
acid can therefore only be effected if care be taken to neutralize 
the acid formed, by the addition of carbonate of lime or the 
like. Besides lactic acid, small quantities of carbonic acid are 
formed ; other products of decomposition have not been 
discovered. 
The influence of different temperatures on the development 
and consequent action of the bacillus is of great practical im- 
portance. Whereas at a temperature below 50° Fahr. no develop- 
ment can be observed, lactic fermentation sets in at 55° Fahr. 
although proceeding very slowly. At 60° Fahr. the develop- 
ment is more active, but it still takes a comparatively long time 
before sufficient lactic acid is produced to coagulate the casein. 
At five degrees higher a very marked difference is seen, and at 
a still higher temperature the progress of fermentation is con- 
siderably accelerated, until the maximum effect is reached at 
about 100° Fahr. With a temperature of 107° Fahr., the 
rapidity of the formation of lactic acid diminishes in a notice- 
able degree, and it ceases altogether at 114° Fahr. 
It has been contended that the bacillus under certain condi- 
tions undergoes some change, resulting in the formation of 
other kinds of cells, and that in its altered state it does not 
cause lactic fermentation, but peptonization of milk. These 
statements must be confuted as erroneous and based upon 
unreliable observations. When working with really pure 
cultivation of the bacillus, no other than lactic fermentation has 
ever been observed ; but it is not an easy matter to get pure 
cultivation, and no other method than that of Koch, previously 
mentioned, is likely to answer the purpose. 
All the experiments made with a view of extracting from 
milk a chemical ferment capable of producing lactic fermenta- 
tion have failed. When lactic acid was produced, the specific 
micro-organism could be found ; and where the latter was 
entirely absent, no formation of lactic acid took place. 
