Such a vast industry, so intimately associated with the food of the bulk of the people, naturally invites the closest study, and, as a consequence, the literature on the subject, which has arisen during the last twenty years, has been of a voluminous character, not only from the point of view of practice, but from that of bacteriology, chemistry, and hygiene.
A pure milk supply is essential to health, and it seems unfortunate that the ordinary milk producer should, in a great many cases, take up an antagonistic attitude to the scientific methods of handling milk. There is a body of opinion being created, however, which is likely to alter this attitude in the next generation, and this is attributable to the fact that so much excellent work has been done at numerous dairy colleges and institutes in all civilised countries that the dairy industry is emerging from a period of rule-of-thumb procedure to its proper place as one of the technical arts.
Transmission of Disease in Milk.—It is not to be wondered at that the handling of milk should now be regarded as a technical business, seeing that milk-borne disease is one of the commonest with which we have to deal.
The commoner diseases which have been transmitted by milk are scarlet fever, typhoid, diphtheria, tuberculosis, sore throat epidemics. Others of a more complex character have been traced to the same source of infection, and the clearest possible evidence has been furnished of the transmission of diseases by means of micro-organisms, which have contaminated the milk supply.
It is therefore necessary to watch over the milk from the source of supply to its consumption. It is primarily on the farm and in the cow-house that methods of handling in a hygienic way should be insisted on, as microbial contamination increases at a prodigious rate, and it is the early microbe therefore which does the most damage.
The milk in the udder, for all practical purposes, may be assumed to be sterile, and the contamination which takes place originates, therefore, from external sources.
One of the principal means of infection is from hairs which fall from the cow into the milk, and many of which are carriers of dangerous micro-organisms.
There is also a certain amount of offensive dirty matter which may fall into the milk-pail, and carry with it undesirable germs.
These impurities may, to a certain extent, be eliminated by good straining, but a surer prevention is to have the cow-house perfectly clean and free from dust, as dust specks are in many cases the vehicles of disease germs. Cleanliness is, in fact, the essential feature in modern dairying, not only in the cow-house, but in the milking utensils, the drainage, etc., and, above all, the milker should be of cleanly habits.
The flavours of milk sometimes arise from the absorption of evil-smelling gases in the cow-house, or from a peculiar taint from certain roots and feeding stuffs, and in such a case it is desirable that aëration should take place in a fresh clear atmosphere, so that oxygenation may have the effect of eliminating and destroying the foreign odours and flavours which may be present. If this process of aëration is carried out at blood heat, the result is generally highly satisfactory.