Page:Popular Science Monthly Volume 90.djvu/383

 Popular Science Alonthly

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���can live under sterile conditions, i.e., in an environment entirely free from bacteria. There are, on the other hand, a number of investigators who believe that bacteria are necessary to the development and health of animals. Madame Metchnikoff studied i^he development of tadpoles, some of which she kept under sterile conditions, [while others she allowed to develop as they do in Nature. After a certain time, she found that those which she kept under ordinary conditions of life weighed six times as much as those which she kept under sterile conditions, which apparently proves that tadpoles can not enjoy the best health without bacteria.

In recent years, bacteria have also been used as curative agents. Metchnikoff's Btilgaricus bacilli, when taken internally, prevent the propagation of harmful bacteria in the intestines. The bacteria which cause intestinal putrefaction can thrive only in an alkaline medium. The Btilgaricus bacilli are acid-producing bacteria. Their

��Above: A view of the entire apparatus de- vised by Professor Michel Cohendy for experiments on animal life in a sterile, bacte- ria-proof environment

��At right: A chick that has served in the ex- periments. The chicks kept under absolutely sterile conditions lost twenty percent of their weight in five days

��Below: Placing the sterilized eggs in the germ-proof incubator where the chicks for development under absolutely sterile con- ditions are hatched

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