II. FEEDING AND IMPLANTATION EXPERI- 

 MENTS WITH WHITE RATS 



The first investigation reported here is an attempt to implant B. acid- 

 ophilus within the alimentary canal of the white rat. The experiments 

 consisted essentially in the feeding, in connection with a basic diet made 

 up of bread and beef, of such special carbohydrates as lactose and 

 dextrin, and of uniform suspensions of B. acidophilus in saline solution. 

 In studying the transforming influence of these agents an effort was 

 made to determine the minimum amounts required to bring about an 

 appreciable change in the intestinal flora. Bacteriological examinations 

 of the feces were made on alternate days. White rats were used ex- 

 clusively. They offer many advantages, at least in this particular 

 instance. They were easily obtained in large numbers, and with little 

 cost to the laboratory; they occupy little room; they may be induced 

 to live on a monotonous and simple diet, and the feces may be obtained 

 fresh at the time they are needed. During the investigation 66 rats 

 were employed, and between 1200 and 1300 fecal specimens were 

 examined. The total number of complete rat experiments was 118, some 

 of the rats being used more than once. 



METHODS 



The rats were kept separately in wire cages having floors made of 

 half inch wire mesh and placed over paper-covered trays for collecting 

 the droppings. The basic diet consisted of bread and beef, ten and 

 three grams respectively daily. This was fed for at least five days 

 prior to the administration of the test substances. The bread and 

 meat diet was found to be sufficient to keep the rats in good physical 

 condition, and was as a rule consumed without waste. There was but 

 one feeding a day, usually in the morning. 



The feces were collected easily according to the method of Hull and 

 Rettger (1917). The rats were held by the tails and gently rubbed on 

 the back. The samples may be collected directly into test tubes with 

 very little or no contamination. The specimens thus obtained were 

 moist and soft and were readily reduced to a more or less uniform 

 suspension by vigorous shaking with the aid of broken glass in test 

 tubes containing ten cubic centimeters of physiological saline solution. 



