The average consumption of new milk is about 15 gallons per head of the population. During the twelve months of 1911, the quantity required for this purpose will be about 682,500,000 gallons, or about 35 per cent. of the total supply; calves will require about 10 per cent. of the supply; the quantity available for butter and cheese will equal about 55 per cent. of the supply.[43] _The Milk Industry in the United States._—In the United States of America, where the habits of the people are somewhat analogous to those in the United Kingdom, it is estimated that the milk from five million cows is annually consumed, which averages twenty-five and one half gallons per year for each person, or equal to an ordinary sized tumblerful each day.[44] 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.