Page:The story of milk.djvu/62

 bovine tuberculosis is hardly ever transmitted to grown persons and seldom to children. Neither is it hereditary. Nevertheless, wherever it is possible to have the herd tested with tuberculin, segregating, if not killing, the animals which show by reaction that they are somewhat tuberculous, it should be done. Milk from such cows should always be pasteurized.

Milk as a Disease Carrier.—A greater danger lies in the fact that, warm as it comes from the cow, milk is an ideal medium for human disease germs to grow in, and may thus become a great conveyor of such germs. For this reason it is of the greatest importance that the milkers are healthy and clean, that the udders and teats be free from dirt, and the milk pail covered as far as possible; the barn must be clean, and every source of infection excluded. This fact also points to the advisability of pasteurization. On page 23 a chart is shown, published by the Toronto Board of Health and indicating the temperatures at which various germs of disease are made harmless.

Bacterial Count.—The test for clean milk now mostly used is the "Bacterial Count," the number of bacteria—or rather colonies of bacteria—found in a cubic centimeter of the milk. It would be better if the nature or quality of the bacteria could be taken into consideration as well as the quantity, but that being as yet impracticable, the next best thing is to depend upon the number. Ordinary good milk often contains hundreds of thousands of bacteria in a cubic centimeter, but where the greatest cleanliness is observed the number may be less than 1,000.

Certified Milk is now sold in many cities which, according to varying city ordinances, is guaranteed to