EXPERIMENTS WITH WHITE RATS 17 



CARBOHYDRATE FEEDING 



In all of the experiments with rats the test carbohydrate was added 

 in dry form directly to the regular diet, namely ground bread and meat. 

 The meals were completely consumed. By comparison of the results 

 of daily examinations with each other and with those obtained during 

 the preliminary period the progressive changes in the intestinal flora 

 could be discerned easily. Each of the carbohydrate feeding experi- 

 ments was carried on for two weeks. 



Lactose. — This sugar was fed to sixteen rats. The ingestion of two 

 grams daily effected a radical transformation of the fecal flora from 

 the ordinary mixed type to one almost entirely dominated by B. acid- 

 ophilus. (See Tables 3 and 4.) A progressive change was clearly 

 evident two days after the first administration of lactose, but did not 

 reach its maximum until at least the fourth day. In some instances six 

 to eight days were required for this maximum. The acidophilus phase 

 persisted with very little or no fluctuation as long as the diet remained 

 unchanged. 



With the actual increase in the numbers of B. acidophilus in the feces 

 there was practically complete suppression or elimination of the types 

 constituting the ordinary mixed flora. Large numbers of the char- 

 acteristic fluffy colonies of the Moro bacillus appeared in the Veillon 

 tubes and agar plates within a few days after the first administration 

 of the lactose, and there was gradual diminution in the amount of gas 

 production in the Veillon tubes until finally it was entirely absent. 

 B. bifidus could be observed only occasionally in these tubes by its more 

 or less typical smooth, disc-shaped colonies occurring in the deeper 

 layers of the whey agar. The direct microscopic examination of Gram- 

 stained films offered additional confirmation of the transition to the 

 acidophilus type of flora. After the first six or eight days the films 

 contained practically nothing but Gram-positive rods. (See Table 3 

 and Chart 3.) 



Table 4 and Chart 4 show the relative numbers of B. acidophilus in 

 the different parts of the intestine. The prominance of the aciduric 

 type, particularly in the lower intestine, is again noteworthy. 



Dextrin. — The sixteen rats employed in the lactose-feeding experi- 

 ments were again placed on the basal diet until the simplified flora had 

 completely given way to the usual mixed type. The rats were then 

 given two grams daily of ordinary commercial dextrin, and the feces 

 examined as before. A change in the character of the intestinal flora 

 became apparent within two to four days. The dextrin stimulated the 

 proliferation of B. acidophilus in the course of the first four to six days 

 to such an extent as to overshadow all other bacterial types. The 

 typical colonies of B. acidophilus became very abundant on the whey 

 agar plates and in the Veillon tubes, often to the exclusion of practically 

 all other forms, and gas was absent from the Veillon tubes. The Gram- 



