EXPERIMENTS WITH WHITE RATS 



23 



picked off whey agar plates, introduced into whey broth and incubated 

 at 37° C. for forty-eight to seventy- two hours. By this simple tech- 

 nique eighteen strains were procured from the rats, and three from 

 human subjects who had been taking 300 grams of lactose daily in 

 connection with their regular diets. 



The bacterial suspensions were prepared by washing off with sterile 

 saline solution the surface growths of large whey agar tubes which had 

 been incubated for forty-eight hours at 37° C. These washings were 

 reduced by dilution to the degree of turbidity corresponding to tube five 

 of the McFarland nephelometer. This bacterial concentration was ad- 

 hered to in all of the feeding experiments in which living bacilli were 

 employed. The final suspensions were added to the basal diet, being 

 thoroughly incorporated in the ground bread. No fewer than three, 

 and as many as eighteen, mixed strains were administered in individual 

 experiments. 



The bacterial suspensions were given in amounts varying from one 

 to five cubic centimeters, and the usual bacteriological examinations of 

 the feces made. After several preliminary trials, beginning with five 

 cubic centimeters, two cubic centimeters of the standardized suspension 

 were finally chosen, as less than this amount was found to be inadequate 

 for bringing about a profound change in the intestinal flora. 



CHART 5 



Curve indicating average percentages of B. acidoph- 

 ilus appearing in fecal specimens from rats 

 fed on a dextrin diet 



Die^ in omms 



Sreod 



Beef 



Dexf/-in 



^Uftyher-ofcJa^ ofjefoe/mi'n/srm^tbn of d/er 



/Z 



/4 



