MILK 197 



tion of bacteria in nature and the channels through which milk may 

 become infected is of much greater importance. It is well for him to 

 bear in mind that wherever life is possible there he may also find 

 bacteria. They are present in the water, in the soil, in the air, in 

 dead animal and plant tissues, on the skin, on the hair, in the upper 

 air passages and in the intestinal tract of man and beast, in excreta, 

 in dust and in dirt, etc. 



Realizing this most liberal distribution of bacteria in nature it 

 is not difficult for the milk producer to understand how they may 

 gain access to the milk. 



But milk, even before it is drawn, has been found to contain 

 variable and often large numbers of these microorganisms. The 

 first source of bacteria in milk is the udder itself. If the animal is 

 suffering from a specific infectious disease such as tuberculosis, an- 

 thrax, foot and mouth disease and other cattle diseases, the bacteria 

 causing these diseases are able to find their way from the animal 

 body through the tissues into the udder. While milk from such ani- 

 mals is utterly unfit for consumption as it imperils the health and 

 life of the consumer, its dangerous effects may be overcome in case 

 of tuberculosis by properly pasteurizing the milk. In the case of an- 

 thrax, however, the germs are very resistant and heating the milk 

 to the boiling point will not destroy them. Fortunately, the milk 

 secretion in animals suffering from anthrax 'decreases rapidly and 

 ceases completely after a few days; the milk takes on a yellow, viscid 

 appearance. The foot and mouth disease, which is causing enor- 

 mous loss of cattle in European countries, has, thanks to the rigid 

 enforcement of our quarantine laws, so far successfully been kept 

 from the herds of this country, hence an infection of mOk from this 

 source is much less liable to occur. 



In healthy animals the only possible channel of bacterial in- 

 vasion is the teat. The teat is a canal surrounded by muscular walls 

 and closed at the extremity by an involuntary sphincter muscle, 

 which varies much in contractility in different animals, often it is 

 so lax that the pressure of a small amount of milk in the canal is 

 sufficient to open it and the animal leaks her milk. In other ani- 

 mals it requires a strong effort on the part of the milker to draw 

 the milk. This canal, with a temperature of the animal body and 

 containing always, even after the most complete milking, a small 

 amount of milk, offers ideal conditions for bacterial growth. When 

 the animal lies down, be it on the pasture or in the stable, the udder 

 and teats come in contact with dust and dirt, which are teeming 

 with bacteria. It seems, then, reasonable to conclude that in case of 

 leaky udders the bacteria adhering to the exterior of the teat have 

 easy access to the interior, where they meet most favorable conditions 

 for rapid development. This assumption is borne out by the results 

 of many investigations which invariably show that cows with leaky 

 udders harbor a very large number of bacteria in their milk. For 

 this reason such cows are discarded from the herd in some sanitary 

 dairies. On the other hand, where the sphincter muscles close the 

 teat firmly the bacterial invasion is greatly checked. 



