INTRODUCTION 3 



higher plants in ordinary circumstances are unable to 

 obtain nutriment unless the complex compounds, pro- 

 teins, urea, and other nitrogenous bodies, which form 

 the important constituents of many manures, are broken 

 down into simpler ones through the agency of bacteria. 

 He sowed seeds in sterile soil free from nitrates, nitrites, 

 and ammonia, which was plentifully watered with sterile 

 milk and solutions of sugar and starch. No changes 

 occurred in these substances, the seeds lost weight, and 

 the seedlings dwindled and died. As regards the higher 

 animals various views have been expressed. Pasteur 

 considered that their life also would probably be im- 

 possible without the presence of bacteria in the intestinal 

 tract. Nencki expressed the opinion that this idea of 

 Pasteur's was an erroneous one, and his experiments in 

 conjunction with Macfadyen and Sieber 1 showed that any 

 considerable decomposition of the food by bacteria first 

 takes place in the large intestine, and that the digestive 

 juices alone, without the co-operation of bacteria, are able 

 to prepare the constituents of the food for absorption. 

 Nuttall and Thierfelder obtained unborn guinea-pigs by 

 Caesarian section with antiseptic precautions, and after- 

 wards kept them in a sterile environment and fed them 

 on sterilised food. Not only did the animals live, but 

 they were even in a more thriving condition than those 

 naturally brought up. The intestinal tract was found to 

 be sterile on the eighth day. Schottelius, however, found 

 that chickens reared on sterile food were retarded in 

 development, and experiments by Moro on turtle larvae 

 point to the same conclusion, viz. that intestinal bacteria 

 are necessary for normal nutrition. On the other hand, 

 Cohendy 2 finds that chickens can be reared perfectly well 

 without the presence of bacteria. Levin found that the 



1 Journ.. of Anat. and PhysioL, xxv, p. 390. . 



2 Ann. de rinst. Pasteur, xxvi, 1912, p. 106. 



