Roger, the eminent successor of Bouchard, described no less than one hundred sixty different species of bacteria which have been found in the alimentary canal. Many of these produce no poisons. Others produce simple organic acids which are under ordinary circumstances harmless; still others produce alcohol, formic acid, butyric acid, and other substances which are unquestionably toxic, although not appreciably so in the extremely minute quantities in which they are produced in the intestine under strictly normal conditions. Still other microbes, of which some scores of species are found in the intestine, produce subtle poisons which are capable of causing deadly effects, even in very minute quantities. Everyone is familiar with the unpleasant effects of the volatile substances which emanate from a mass of putrefying flesh. Headache, nausea, and other symptoms may result from the odors alone which arise from putrescent substances. These volatile substances are poisonous, but other non-volatile poisons present are much more active. Some are almost as powerful as the venoms of snakes, which they resemble in chemical composition. The South American Indian poisons the points of his deadly arrows by dipping them into putrid flesh. Butchers as well as undertakers sometimes die as the result of a small cut made with a knife soiled by contact with a dead body. The same poisons are produced when putrefaction takes place in the intestine.

None of the intestinal microbes are essential for life or health. Pasteur supposed that all life was dependent upon microbes. One of his pupils, Roux, showed this idea to be erroneous, at least as regards vegetables, by causing beans to grow in sterile soil and sterile water. Pasteur admitted his error in regard to vegetable organism, but still maintained that animals could not live without the aid of intestinal bacteria. Nuttall and Thierfelder, by experiments with guinea pigs, showed that these animals could be brought into the world free from germs, and made to grow on food which contained no trace, of bacteria. When the animals were killed, no bacteria were found in their intestines. Recent experiments made by Roux showed that chickens hatched and grown under sterile conditions thrived better than chickens hatched under ordinary conditions.

Numerous other experiments have confirmed this fact, but most important of all were the observations of Levin at Spitzbergen, in the Arctic region. This observer made careful examination of scores of Arctic animals, and found that in the majority of cases no bacteria were present in the intestine. This fact will be easily understood when the additional fact is known that the air, and even sea-water, are in these cold regions practically free from bacteria.

The fact that bacteria are present in the human intestine is therefore no evidence that they supply any human need. The presence of these minute parasites is, instead, an unfortunate incident of our existence. Metchnikoff has shown that colon germs in no way contribute to our well-being, but on the contrary, are an undoubted cause of premature senility, and the unnatural abbreviation of human life, the sad lot of the average man.