388 
Micro-organisms and their Action 
are inclined to look on the causes of blue milk as not being 
due to pathological conditions of the cow, but rather to external 
influences acting upon the milk after it has been drawn from 
the udder. It has been fully proved that the production of 
blue-coloured milk is due to the action of a micro-organism. 
If nutritive gelatine be inoculated with blue milk, the growth 
of colonies will be observed. The colonies differ in appear- 
ance, some forming spots of a pure white, others of a yellowish 
white colour, the gelatine surrounding the latter being of a 
greenish tint. If these colonies are used separately for the 
inoculation of milk, those samples only which contain the 
micro-organisms of the yellowish white colonies will get blue. 
On raising pure cultivations of this micro-organism it is 
found to be a bacillus, which multiplies by dividing ; the cells 
separate, and move about singly, and at last form spores, not 
more than one spore being formed by a single cell. Upon 
milk which has been inoculated, intense blue patches are seen 
to appear at about the same time that the milk gets sour. The 
slower the lactic fermentation proceeds, the more the patches 
spread out, and the better their colour develops. Blue milk 
reaches a less degree of acidity than other milk. 
If perfectly sterilized milk be inoculated, the appearance is 
different. The milk does not turn sour, but remains liquid, 
and shows after a time alkaline reaction. The coloration com- 
mences on the cream, and spreads more and more, gradually 
working downwards through the whole of the liquid. In case 
the milk had been slightly sour when sterilized, the colour will be 
a light blue, but in case the reaction of the milk had been 
amphioteric, the milk will assume a slate colour, which turns 
into a bright blue upon the addition of an acid. The brilliant 
blue colour is not produced unless there is some free acid 
present. The bacillus, however, does not give rise to the 
formation of lactic or butyric acid, but, on the contrary, seems 
to live upon them if present, for slightly acid milk gradually 
becomes neutral and even alkaline. ^ 
The reas(?n why in milk the blue colour makes its appear- 
ance in smaller or larger patches, while in sterilized fresh milk 
it diffuses itself throughout the whole mass of the liquid, is to 
be found in the fact that the bacillus acts upon the casein, and 
that where the latter is coagulated the action gets localized to 
some extent. That the milk-sugar is not attacked has been 
proved by its undiminished quantity. Pure solutions of casein 
assume a slaty colour after inoculation, as also do solutions of 
other substances containing nitrogen. In certain solutions a 
green colour is produced. 
The b;)(i]his does not develop at a temperature below 
