590 GASTRO-INTESTINAL BACTERIOLOGY 



flora in health is the chemical composition of the ingested food. 1 

 Escherich, 2 as far back as 1887, clearly showed that a very charac- 

 teristic change in the intestinal flora of dogs could be brought about 

 by feeding protein, during which bacteria that liquefy gelatin become 

 abundant in the feces. 



Assuming that food is an important factor in determining the more 

 common types of bacteria found respectively in the intestinal tracts 

 of nurslings, artificially fed children and adults, it would be reasonable 

 to expect that the same or similar bacteria should develop in the 

 intestinal tracts of experimental animals, provided they were fed upon 

 the same foods as nurslings or adults. A prolonged series of experi- 

 ments upon monkeys, 3 dogs and cats have shown that alternations in 

 diet do influence the prevailing types of bacteria in the intestinal 

 tract to a marked degree. The essential features of these experiments 

 were that monkeys, dogs and cats fed upon cow's milk containing 

 sufficient lactose solution to bring the percentage of protein and 

 carbohydrate approximately to that of human breast milk excreted 

 feces which, in appearance and in bacterial content, approached very 

 closely those of the normal human nursling. The acid reaction, prac- 

 tical absence of obligately proteolytic bacteria, the dominance of 

 Bacillus bifidus and acidophilus and the appearance of Micrococcus 

 ovalis in numbers similar to corresponding types in normal nurslings' 

 feces were in striking contrast to the feces of the same animal after 

 a prolonged feeding with a purely protein diet. In the latter event 

 large numbers of proteolytic bacteria were present in the feces, which 

 were alkaline in reaction and rich in indol, phenols, hydrogen sulphide, 

 ammonia and other products indicative of intense proteolytic decom- 

 position. Obligately fermentative bacteria of the bifidus-acidophilus 

 type were few in number, or practically absent. Recently Rettger 4 

 has made somewhat parallel observations in mice and rats. 5 



The nature of the dominant organisms which develop in diets rich 

 in carbohydrate varies with the carbohydrate itself. Bacillus bifidus 

 is more commonly predominant when lactose is the sugar fed, without 



1 See Kendall, Jour. Med. Research, 1911, xxv, 136, for resume. 



2 Darmbaktericn, etc., p. 111. 



3 Kendall, Jour. Biol. Chem., 1909, vi, 499. Herter and Kendall, ibid., 1910, vii, 203. 

 Kendall, Jour. Med. Research, 1910, xxii, 153; ibid., 1911, xxiv, 411; 1911, xxv, 117. 



4 Centralbl. f. Bakt., prig., 1914, Ixxiii, 362. 



6 It is rather more difficult to replace a proteolytic flora in adult animals by a fer- 

 mentative flora than it is in young animals of the same species; the explanation of this 

 relative refractoriness to substitution of obligately fermentative types of bacteria for 

 the facultative organisms commonly found in the intestinal tracts of the older animal 

 is by no means clear. 



