EXPERIMENTS WITH HUMAN SUBJECTS 85 



TRANSFORMING INFLUENCE OF MILK CULTURES OF 

 BACILLUS ACIDOPHILUS ON THE INTES- 

 TINAL FLORA 



In the more recent experiments on intestinal implantation B. acidoph- 

 ilus was administered in the form of pure milk cultures. The strains 

 which were employed were the same as in the preparation of the whey 

 agar cultures previously described. Since B. acidophilus is primarily 

 of intestinal origin, and not a milk-borne organism, many difficulties 

 were encountered in the preparation of the sour milk. However, within 

 three weeks the strains employed were by frequent and liberal transfers 

 from milk to milk adapted to the new environment, so that ten cubic 

 centimeters of inoculum added to one liter of sterile milk effected dis- 

 tinct acidification and creamy coagulation within twelve to fifteen hours 

 at 35 to 37° C. A full description of the method of acclimating B. 

 acidophilus, and of preparing and utilizing the sour milk culture will 

 be found in one of the following chapters. 



The B. acidophilus milk was given to quite a number of subjects, of 

 whom some received 500 cubic centimeters and others one liter daily, in 

 addition to the regular diets. The milk cultures were taken as a rule 

 in 500 cubic centimeter quantities, and between meals. Occasionally the 

 daily amount was divided and the portions taken at definite intervals. 



Subject A whose intestinal flora was easily simplified by any and all 

 of the transforming agents employed throughout the investigation, 

 responded readily to the consumption of 500 cubic centimeters of the 

 acidophilus milk per day (Table 48). B. acidophilus soon made its 

 appearance and in a very short time became the dominant and practi- 

 cally the sole viable organism occurring in the stools. After the first 

 two days of sour milk feeding no gas was produced in the Veillon tubes, 

 and the stained slide showed a sharp increase in the Gram-positive rods 

 of the aciduric type, which soon reached 75 to 80 per cent of the total 

 number of fecal organisms counted. After the discontinuance of the 

 sour milk feeding the flora gradually reverted to the ordinary mixed 

 type. This return required about five days. 



Again, the ingestion of the same amount of the milk culture (500 

 cubic centimeters) daily by subjects F and G exerted only a slight 

 transforming influence on the fecal flora. (See Tables 49 and 50, and 

 Chart 36.) The whey agar plates and Veillon tubes indicated a moder- 

 ate multiplication of B. acidophilus, and the stained films showed the 

 Gram-positive rods to be outnumbered by the other types of intestinal 

 organisms. However, when one liter of the acidophilus milk was taken 

 daily by these same subjects the complex intestinal flora was practically 

 completely reduced in a few days to the aciduric type. (See Tables 51 

 and 52, and Chart 37.) Abundant proliferation of B. acidophilus was 

 clearly evident after four to six days, and its complete predominance 



