When you put the point of your pencil into your mouth, you will leave germs on it just as you do on the edge of a cup when you drink. Never put your pencil into your mouth; never use any other person's pencil; never trade pencils.
(3) By the common bite
Sometimes we see a child giving his friends a bite of his apple or candy or cake. Of course when disease germs are in the mouth of the one who takes a bite, the germs will be left on the apple, candy, or cake. By no means should a boy or girl be selfish, but if you have something to share with your friends, break it or cut it into pieces. Never take into your mouth anything from which another person has taken a bite.
How tubercular cows cause consumption
Milk that comes from consumptive cows may contain the germs that cause tuberculosis. When you drink the milk from such cows, you take these germs into your body. They find their way from the stomach and intestine into the blood, and there they travel about until they find a spot where the cells are dead or are not doing their work properly. When they find such a place, they settle down and begin to grow; and the first thing you know, you will have tuberculosis in that part of your body. Sometimes the germs do not have to go out of the stomach or intestines to find a favorable opportunity to take hold and grow. When this happens, we have consumption of the bowels.
One cannot tell by looking at milk or by tasting it whether or not the germs of tuberculosis are present. They do not make the milk sour; neither do they make it look different from pure milk.
One cannot tell by looking at a cow whether or not she has tuberculosis. Sometimes a cow will have tuberculosis and yet look very healthy. There is, however, a way by which we can tell when a cow has this disease, no matter how healthy she may look. This is what is known as the tuberculin test.
How to detect tuberculosis in a cow
If a little tuberculin is injected under the skin of a cow that has tuberculosis, it will make her have a fever and appear sick for a day or two. If she is free from tuberculosis, it will not make her sick at all.