382 
Micro-organisms and their Action 
Butyric Ferment. — It has been observed that in milk sub- 
jected to heat with a view of preserving it, coagulation of the 
casein takes place after a time. Upon examination it is found 
that the reaction of the milk is alkaline, and that it contains 
no lactic acid. In such milk, when examined by the aid of 
the microscope, a bacillus is found, which even on superficial 
observation is distinguished by its larger size from the bacillus 
which causes lactic fermentation, and the action of which upon 
milk is very different. 
If sterilized milk be inoculated with this organism, as 
obtained in pure cultivation, and exposed to a temperature of 
100^ Fahr., certain changes will become visible on the second 
day. A light yellowish liquid is noticed below the cream layer, 
which is a sign of the beginning of the precipitation of the 
casein. The volume of this liquid extends downwards more 
and more, the top part nearest to the cream becoming quite 
clear, while the lower portion remains cloudy and covers a 
coagulum of precipitated casein. The quantity of the latter is 
gradually diminished with the length of time the experiment is 
continued. 
Upon examination, the liquid formed is found to contain 
several products of decomposition of casein, such as leucine, 
tyrosine, and ammonia, while at the same time a slightly 
bitter taste is observed. 
The action of the ferment can best be described as causing, 
first, the coagulation of the casein in a similar manner to rennet, 
and then exercising a peptonizing influence by which the casein 
is transformed into soluble compounds. Besides these chemical 
changes, the same bacillus is able to effect a perfectly different 
change if the conditions be varied. This bacillus is unable to 
act either upon milk-sugar in its unaltered state, or upon free 
lactic acid, as free acid interferes with its development. If 
however it is brought in contact with a solution containing 
inverted, or hydrated, milk-sugar, or salts of lactic acid, a 
fermentation is set up, by which butyric acid is produced. 
When speaking of lactic fermentation we mentioned that it 
was preceded by a hydration of the milk-sugar. Butyric acid 
can therefore be formed in unpreserved milk, and the same 
action takes place in solutions of other sugars, starch, and 
similar substances. The presence of increasing quantities of 
the butyric acid formed does not appear to interfere with the 
further growth of the ferment. 
The very fact that in milk which has been successfully 
preserved against lactic fermentation the alteration described 
above can take place, proves that the bacillus which cause's 
butyric fermentation has a greater resisting power against heat 
