28 QUEENSLAND AGRICULTURAL JOURNAL, [1 Jay., 1899. 
as thunder or lightning, has any effect. All the evidence indicates that the 
increased tendency toward the formation of lactic acid is due to the more 
favourable growth conditions that obtain at sucha time. ‘The warm, muggy 
atmosphere favours rapid germ development, and consequently the souring 
changes occur more quickly. 
MIXING NIGHT AND MORNING’S MILK. 
A well-established rule of dairy practice is not to mix the night and 
morning’s milk, or, to put it on a broader basis, fresh and old milk. Common 
experiences teaches that this mixture is apt to sour much more rapidly than 
where the two milks are left separate. The reason for this is a physical one, 
and is based on the difference in temperature of the two lots, and the relation 
that these temperatures bear to the bacteriai life that is contained in each milk. 
Under normal conditions the older the milk is the richer it is in germ life. 
but the night’s milk is usually cooler than the morning’s milk, which is 
relatively deficient in germ life. The mixture of the two lots raises the 
temperature of the whole mass, and at the same time increases the germ 
content of the fresh milk so that fermentative changes occur more rapidly. 
If night’s milk at a temperature of 55 degrees Fahr. contains 1,000,000 
bacteria per cc., and the morning’s milk, at a temperature of 80 degrees Fahr., 
has only 20,000 organisms per cc., the mixture of the two in equal volumes 
would raise the temperature to about 65 degrees. At this temperature the 
510,000 bacteria in the mixed milk would grow more rapidly than the 1,000,000 
at a lower temperature, and would, therefore, sour the same sooner. 
HOW CAN WE DETECT BACTERIAL FROM OTHER TAINTS ? 
Before one can intelligently search for the cause of the taintin milk, he must 
have some idea as to the character of the same. A tainted condition arising 
from any source injures the quality of the product, but the effect of a taint is 
largely determined by its character. 
Taints may be classified into two groups depending upon their origin— 
1. Those produced by bacterial fermentations in the milk ; 
2. Those caused by the absorption of odours directly from the animal, or 
after the milk is drawn. 
In the minds of most dairymen, the latter class has been considered the 
more important, and the effect of the first group has not been adequately 
recognised. Asa matter of fact, a larger number of taints, that affect the 
quality of milk, are induced by bacterial growth than otherwise. The danger 
that comes from this class is, that it is caused by a living organism, and, there- 
fore, may be widely distributed unawares. A physical taint is unable to 
reproduce itself, so that a mixture of tainted milk with a larger quantity of 
normal milk serves to diminish the intensity of the taint. 
The manner in which the respective taints are produced enables one to 
detect the difference. If produced by germ origin, a well-marked taint in any 
milk can be propagated from one batch of milk to another, by transferring a 
small quantity and placing it under conditions that favour bacterial growth. 
Particularly is this true, if the inoculated milk is first heated to destroy pre- 
existing bacteria. If it has been directly absorbed from some external source, 
it cannot be transferred in this way. 
Then, again, if a taint is produced by biological causes, it will not, 
ordinarily, appear until some time after the milk is drawn; for, as a rule, 
bacteria gain access to the milk subsequent to its withdrawal, and a certain 
period of incubation must elapse before the taint-producing organism can 
increase in sufficient numbers to produce the obnoxious odour or flavour. If 
the defective condition of the milk is due to direct absorption from the animal, 
as is the case where the food contains volatile odour-producing substances, then 
it will be noted immediately aiter milking. Aeration of the milk is often 
recommended in such cases, but sometimes the odour is so persistent that this 
fails to eliminate it, 
