Popular Science Alonthly 



367 



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 



