( Originally Published 1938 )
Before we see how the waste is eliminated, we should say a few words on the bacteriology of the intestines, for it is a matter of considerable importance. At birth the gastro intestinal tract of an infant is sterile, but shortly after various bacteria appear in the feces. These vary in type until the child is fed a general diet. The character of the bacteria flora then changes, and remains fairly constant for the rest of the individual's life. It varies to a certain extent, however, with the character of food consumed and with the implantation of disease bearing organisms, such as the dysentery bacillus.
In the intestine there is a large number of bacteria which progressively increases as we go downward, until we find the large intestine literally swarming with them. Generally speaking, there are three or four main types of bacteria. The Bacillus coli communis, or in English, the common bacillus of the intestine, as the Latin name signifies, is the most regularly and frequently found. Other bacteria regularly found are those that produce gas and those that produce acid. The predominance of one group over another may be affected by changing the content of the diet a protein diet favors one type, a starch diet another.
The stomach is nearly always sterile since the acid nature of the gastric juice, as we pointed out, destroys most of them.
It has been estimated that each day's food in its passage through the alimentary canal is subject to the action of over a hundred billion bacteria. As we have said, these are chiefly found in the large intestine. Since they are regularly present, scientists have endeavored to ascertain whether they perform some beneficial function in connection with digestion. It is now generally believed that those bacteria which are habitually found help to protect the normally healthy individual against the invasion of the harmful types. Bacillus acidophilus is considered the type that is best fitted for this important function. Milk, fruit and vegetables, as well as lactose and dextrin, favorably affect the intestinal flora, as its bacterial content is called, by decreasing the amount of intestinal putrefaction. Cultures of the acidophilus bacillus combined in milk, candy and other forms of food may be taken to establish and maintain a healthy condition in the intestines.
So here we have another important reason for keeping the intestines in good working order: in every healthy individual there is a stalwart and numerous army constantly thwarting the invasion of enemy bacteria.