390 
Micro-organisms and their Action 
up part of the lactic acid formed, and thus enables the bacillus 
of lactic fermentation to decompose a larger quantity of the 
milk-sugar present. 
Preservation. — In the preceding pages an account has been 
given of those micro-organisms which at the present moment are 
recognised as exercising a definite fermentative action on milk. 
In places where milk is constantly kept, it must be expected 
that at least some of the organisms described will be present in 
abundance, and the utmost cleanliness is therefore necessary in 
order to keep them in check, so that they cannot interfere in 
too serious a manner. It must not be supposed, however, that 
besides those mentioned other organisms do not occur. When- 
ever milk comes in contact with the atmosphere, as it does 
largely when being handled, it must also come in contact with 
germs floating about in the air, and retain a number of them. 
The more contaminated the air, the greater number of germs 
will the milk retain. When cows are housed, more foreign 
matter may be expected to enter the milk than when they are 
out on grass, and it is a common observation that, unless special 
precautions are taken, milk from stall-fed cows generally is found 
to contain a sediment consisting of dust of food and the like. 
The spores of mildew are frequently present in this sediment, 
but pernicious as these parasites are to the plants which they 
inhabit, they are not known to have any injurious effect on 
the milk. 
Other organisms which may find milk a suitable medium to 
thrive in do not seem to set up in it a fermentative decompo- 
sition, and therefore do not come strictly within the scope of 
this paper. But although the milk may not be affected by 
their presence and development, they may have a very delete- 
rious effect upon the consumer of it. The subject of the 
spreading of infectious diseases through milk containing the 
contagium of those diseases has of late been brought before 
the public very prominently and upon numerous occasions. 
For this reason, and because what we shall have to say with 
regard to the checking or destroying of the micro-organisms 
refers alike to all of them, we venture briefly to touch' upon 
this question. 
Although it can by no means be said that in all the cases 
in which epidemics have been assigned to infected milk, it has 
been proved beyond doubt that another common cause could not 
have existed, and that milk was indubitably the means by which 
the contagium had been carried and communicated to the 
sufferers, it must be admitted that in some cases the evidence 
obtained has pointed so strongly and exclusively to a common 
milk-supply that it had to be taken as proof conclusive of 
