696 ARTHUR ISAAC KENDALL 



selective effects of various carbohydrates upon the types of lactic acid pro- 

 ducing microbes which become dominant in the intestinal tract as one or 

 another sugar is added to the diet. 



A more recent scries of observations by Torrey has not only amplified 

 this particular aspect of the subject and confirmed anew the principle 

 of the bacterial response to dietary alternations, it has also shown that 

 fats play a very minor, or entirely negligible, part in this process. 



In general, therefore, it may be stated that the normal nursling in- 

 testinal flora is essentially fermentative in character. It represents the 

 natural bacterial response to a definite nutritive condition created within 

 the alimentary canal by the continuous passage of milk sugar lactose 

 throughout the absorptive area. Furthermore, it is possible to reproduce 

 essentially the same chemical activities and bacterial types in the in- 

 testinal tracts of experimental animals, both carnivora and omnivora, by 

 the administration of the diet of the normal nursling. 



2. Adolescent and Adult Intestinal Bacteriology 



Adolescents and adults, unlike nurslings, are normally omnivorous. 

 The proportions of proteins and carbohydrates [principally starches and 

 dextrins] in the average adolescent and adult diet are more nearly. equal 

 than is the case with nurslings or milk-fed children. The large intestine, 

 from the cecum to the rectum, therefore, becomes more and more a 

 receptaculum of the products of protein digestion, and of protein deriva- 

 tives altered by bacterial digestion. The tendency is for putrefactive 

 processes to predominate, due to the more or less periodic intervals of 

 carbohydrate disappearance. These periods of carbohydrate presence and 

 absence exercise a very decided influence upon the types of bacteria 

 which can thrive under these intervals of carbohydrate and protein offer- 

 ings for energy. The. obligate lactic acid flora, either Bacillus bifidus 

 or Bacillus acidophilus, according to Moro, Finkelstein, and the author, 

 dies out and the succeeding bacteria are of the colon type, which, as has 

 been stated before, can utilize protein for energy nearly as well as 

 carbohydrates. 



Organisms of ike Bacillus coli type, in fact, are the dominant bacteria 

 of the intestinal and fecal flora in normal adolescents and adult life, 

 when the ordinary mixed diet is that of the dweller of the temperate 

 zone. Under such conditions some indol is formed in the alimentary tract 

 and in many individuals at least more frequently those who are heavy 

 protein eaters it will be found as indican in moderate amounts in the 

 urine. 



The conditions under which indol is formed are also favorable to 

 the formation of aromatic amins, as histamin, indol ethylamin, or even 



