Milk as a carrier of germs
Milk has carried the germs of every disease of which the germ is known; it has also carried many diseases of which we do not know the germ. Disease germs grow rapidly in milk, and they do not make the milk look different or taste different from milk that is perfectly pure. If you could take two bottles of milk entirely free from disease germs and put typhoid fever germs in one, and should set both bottles in an ice box for twenty-four hours, you would not then be able to tell into which one you had put the germs. The milk in both bottles would look and taste just the same. The only difference between the milk in the two bottles would be that if you drank from one it would make you stronger and would furnish you with both building material and power-producing material, while if you drank from the other you would become very ill and would probably die.
How disease germs get into milk:
Since we cannot tell from the taste or the appearance of milk whether or not there are disease germs in it, we must take every precaution possible to keep them out. The first step is to learn where the disease germs come from and how they get into the milk.
Fig. 13. Polluted milk is sure to come from a dairy where cleanliness is not observed.
(1) By dirt on the cow
Every cow has more or less dirt on her sides and udder; some have a great deal. When the cow is milked, much of the dirt falls into the milk bucket. This dirt always contains a great many germs of different kinds, and many of them are germs that cause disease. Straining the milk will take out much of the dirt, but disease germs will go through the finest strainer that was ever made.
In Figure 13 we see a man milking a dirty cow. The owner has allowed his lot to become so dirty that the cow cannot find a clean place in which to lie down. If the man kept his lot clean, and if before milking the light dirt on the cow's sides and udder were wiped off with a damp cloth, no germs would fall into the milk.
(2) By dirt in the cow barn