on Milk and Milk-Products. 
389 
50° Fahr. Between 50° and 55° Fahr. its action commences, 
but only in a slight degree. The most suitable temperature is 
from GO^ to 65° Fahr, Above 65^ Fahr. there is observed a 
decrease in the time, but no increase in the intensity of 
colour. With a temperature of 77° Fahr. the power of acting 
further decreases, and it ceases altogether at 99° Fahr. 
The assumption that the milk or its colouring principle is 
poisonous is in no way supported ; on the contrary, experi- 
ments have shown that small animals which were fed upon 
blue milk, or injected with the pure cultivated bacillus, did not 
suffer any harm. The assumption is based on the belief that 
the blue colour is an aniline colour, and that all aniline colours 
must be poisonous. The latter is not at all the case ; and as to 
the character of the coloration of blue milk we know nothing 
up to the present. 
• As far as the formation of pigments on or in milk is concerned, 
" blue milk " appears to be the only phenomenon of its kind 
which has attracted general attention, and the cause of which 
has been thoroughly studied. The bacillus described is, how- 
ever, not by any means the only one which can produce a 
certain colour in milk, as there exists another bacillus which 
in its form and action upon milk very closely resembles the 
bacillus of blue milk, but produces a slight green coloration. 
A third bacillus also colours milk yellowish green, but at the 
same time coagulates, and in its further progress peptonizes 
the casein. A fourth also acts in exactly the same manner 
on the casein, producing spots which are in the first place of 
a deep blue colour, and gradually become darker until they 
are almost black. There are known, furthermore, two forms 
of micrococci, the one coagulating the casein, but not ex- 
hibiting any peptonizing power, and colouring the milk yellow 
to orange, the other producing a colour of an intense red. 
Oidium Lactis. — This fungus is mentioned here because to 
it effects have been ascribed which in truth are produced by 
one of the micro-organisms mentioned above. The fungus, 
which forms a thick growth of white colour, is invariably 
found on sour milk, and this fact has led to the belief 
that to its presence is due the production of lactic acid and 
the coagulation of the milk. Although the fungus prefers for 
its growth slightly acid media, it develops rather luxuriantly 
also in neutral, but indifferently in alkaline substances. The 
most suitable temperature is from 60' to 70^ Fahr. If sterilized 
milk be inoculated with the purely cultivated fungus, it remains 
fluid, does not get sour, but, on the contrary, becomes slightly 
alkaline. There can be no question that the fungus has no 
connection with lactic fermentation, except perhaps that it uses 
2 D 2 
