646 BACTERIA OF THE INTESTINAL TRACT 



the feeding of milk or lactose to rats, in addition to the regular diet of grain and vege- 

 table feed, causes a profound change in the intestinal population. When as much as 

 3 gm. of lactose was given daily the bulk of the flora consisted of L. bifidus, but when 

 the amount of this sugar was reduced to 2 gm. a day L. bifidus gave way to L. acid- 

 ophilus, which continued as the dominant organism as long as the lactose was fed. 

 They concluded that milk owes its transforming influence to the lactose. 



Torrey' showed that in the administration of lactose, 250-300 gm. were required 

 to transform the intestinal flora of typhoid patients from the usual mixed to one domi- 

 nated by L. acidophilus. 



Distaso and Schiller^ claimed that of the various carbohydrates employed by them 

 lactose and dextrin alone are. able to transform the flora. These observations were 

 confirmed and extended by Rettger and Cheplin.^ 



TRANSFORMATION OF INTESTINAL FLORA: HYGIENIC 

 AND THERAPEUTIC ASPECTS 



The earlier observations that diet has a large determining influence on the nature 

 and kinds of micro-organisms developing in the digestive tract have been fully con- 

 firmed and very materially extended in recent years. The present renewed interest 

 in this field has been stimulated by the investigations conducted in this country, 

 particularly in the laboratories of Yale University. Reference to some of these has 

 already been made in this chapter. Space does not admit of a complete review. 



The intestinal flora of white rats can be regulated almost at will. When fed on a 

 diet consisting largely of mixed grain (corn, oats, and sunflower seed), a large propor- 

 tion of the intestinal population is made up of L. acidophilus, as is seen by the direct 

 microscopic and by the plate-culture method. On changing the diet to bread and 

 meat, a more or less complete change in flora to the non-aciduric, and in a large meas- 

 ure gram negative types, occurs within two to three days. A reversion to the aciduric 

 phase may be effected again by the feeding of from i to 3 gm. of lactose or dextrin 

 daily, in addition to ground bread or dog biscuit. 



In spite of the earlier claims of some investigators, lactose and dextrin alone of 

 the ordinary carbohydrates are able to bring about this transformation. The energy 

 requirements of L. bifidus are much greater than those of L. acidophilus, and therefore 

 appreciably more lactose and dextrin must be administered to stimulate the Tissier 

 bacillus than L. acidophilus. Hull and Rettger-* found that the flora may be trans- 

 formed also by milk feeding, though a longer time is required, and the change to the 

 aciduric type is not as nearly complete as when lactose is used. 



Human subjects respond to the same influences, though as a rule not so readily. 

 Rettger and Cheplin^ were able as a rule to effect pronounced and at times almost 

 complete transformation in the normal subjects employed, by the administration of 

 300 gm. or less of lactose or dextrin daily. 



Transformation from the mixed to the aciduric type was further accomplished by 



• Torrey, J. C: loc. cit. 



- Distaso, A., and Scliiller, J.: Compt. rend. Soc. de biol., 76, 243. 1914. 



■' Rcttf^cr, L. F., and Chcplin, H. A."- Intestinal Flora. New Haven: Yale University Press, 192 1. 



4 Hull, T. G., and Rcltgcr, L. F.: loc. cit. 



s Rettger, L. F., and Cheplin, H. A.: loc. cit. 



