360 
by the simultaneous action of the simple ferments. Enterococ- 
cus has been found to be the species predominantly producing 
inactive lactic acid, valerianic acid, and also always acetic acid. B. 
coli follows in its action, producing laevo-lactic acid. Together these 
two organisms give an acidity to milk equivalent to 1.47 to 2 per 
cent of sulphuric acid. This degree of acidity arrests the action of 
the proteolytic ferments and brings on the coagulation or curdling 
of the milk. The B. acidi paralactici continues the destruction of 
the lactose, however, and gives rise to the true lactic acid fermenta- 
tion, producing always dextrolactic acid. The medium having 
become favorable for its growth and development the Bacillus lac- 
topropylbutyricus sets up its characteristic fermentation, producing 
always inactive lactic and also propionic and butyric acids until 
a total acidity of 4 to 6 per cent in terms of sulphuric acid is 
reached. This degree of acidity arrests all bacterial action. The 
fungi, oidium lactis, and rhizopus nigricans then intervene, however, 
and bv oxidizing the organic acids and lactose and bv effecting a 
further destruction of the casein again favor the growth and multi- 
plication of those organisms whose development has been momenta- 
rily checked. It also appears from the work of Tissier and Gaschmg 
that the simple ferments alone can bring about the decomposition of 
the casein and its ultimate derivatives. They have further observed 
that the bacteria ordinarily concerned in the souring of milk are not 
in any way directly responsible for the digestive disturbances which 
occasionally result from the use of milk as a food. Under certain 
conditions, however, they may act as predisposing causes, but the 
accidents of botulism are due, according to these authors, to special 
species of organises differing from those which are ordinarily con- 
cerned in the souring of milk. 
Quite recently Beyerinck (21) has again discussed the lactic fer- 
mentation of milk. He has found that temperature and oxygen 
pressure determine the nature of the autofermentation of milk. At 
temperatures below 40° C. the fermentation brought about by B. 
coli is replaced by a butyric acid fermentation, which, after lasting 
some time, is succeeded by a lactic acid fermentation. In good milk, 
even at 40° C., at which temperature gas-producing bacteria develop 
most rapidly, no gas is produced. This fact therefore forms the 
basis of a dairy test for judging of the purity of milk. He recog- 
nizes three forms of lactic acid fermentation depending on the tempera- 
ture. At very low temperatures there occurs the slimy lactic acid 
fermentation, which, according to this author, is due to the smaller 
cell walls of the organism. At medium temperatures the common 
lactic acid fermentation predominates, this being caused by the lacto- 
coccus and at higher temperatures the lactic acid fermentation 
