EXPERIMENTS WITH WHITE RATS 49 



the experiment. The transformation of the flora was practically com- 

 plete in each of the three groups of rats, and B. acidophilus was present 

 in the fecal specimens to such an extent as to almost completely exclude 

 all other types. The examination of the different sections of the intes- 

 tine showed the presence of B. acidophilus throughout the length of the 

 digestive tube, and in relatively large numbers.* 



B. ACIDOPHILUS VERSUS B. BULGARICUS FEEDING 



The methods of preparing and administering the suspensions of living 

 organisms in these experiments were identical with those employed in 

 the preceding work. The five strains of B. bulgaricus which were used 

 were isolated from commercial preparations placed on the market by 

 five different laboratories. The strains of B. acidophilus were the same 

 as those employed in the previous experiments. 



Since two cubic centimeters of the standard suspension of B. acidoph- 

 ilus, as well as one cubic centimeter of the same suspension reinforced 

 with one gram of lactose, were found to effect profound transformation 

 in the flora of the albino rat, parallel sets of experiments were set up in 

 which the administration of B. bulgaricus and attempts to recover this 

 organism from the feces constituted part of the plan. 



As it is now a well-known fact that colony formation, morphology, 

 staining properties, etc., are unsatisfactory bases for distinguishing 

 between B. acidophilus and B. bulgaricus, and that even the milk acidity 

 test is not always dependable, the fermentation test of Rahe (1914) 

 was employed. The pure strains of these two organisms were inoculated 

 into maltose broth adjusted to pH 6.8, and incubated at 37° C. for 

 forty-eight to ninety-six hours. The maltose solution and the broth 

 were sterilized separately. None of the five laboratory strains of 

 B. bulgaricus were able to attack the maltose with acid production, 

 while all of the many strains on hand of B. acidophilus fermented the 

 sugar with sufficient production of acid to be readily demonstrable. 

 This method of distinguishing between the two types of aciduric bac- 

 teria has been of very material assistance in the carrying on of this 

 phase of the investigation. 



In all of the experiments in which B. bulgaricus was administered its 

 ingestion had absolutely no influence on the character of the intestinal 

 flora. At no time during the entire investigation was B. bulgaricus 

 recovered from the feces, regardless of whether the suspension was fed 

 alone or in the presence of lactose as an energy-supplying pabulum. In 

 all of the animals receiving the bulgaricus suspension alone the usual 

 mixed flora prevailed to the end of the feeding experiment. Upon the 



*For a complete record of results the reader is referred to the doctorate thesis of 

 H. A. Cheplin in the Yale University Library. 



