210 



SCIENCE 



[N. S. Vol. XLII. No. 1076 



teria in the normal infantile feces. There 

 appears to be a definite relationship be- 

 tween the high percentage of lactose, the 

 dominance of an obligately lactic acid-fer- 

 menting organism, and the absence of 

 putrefactive bacteria in the normal in- 

 fantile intestinal flora. This infantile 

 flora, furthermore, appears to be a protec- 

 tive one in the sense that it inhibits the 

 growth of bacteria which might produce 

 either putrefaction or disease. These 

 latter organisms are somewhat intolerant of 

 lactic acid. It may be remarked paren- 

 thetically that one of the first indications 

 of intestinal disturbance in infants is the 

 temporary or even permanent disappear- 

 •ance of this lactic-acid flora. 



B. hifidus is an organism which does not 

 thrive in artificial media in the absence of 

 sugars, and it is not surprising to find, 

 therefore, that as the breast-fed infant be- 

 comes older and its dietary demands more 

 varied, B. hifidus tends to disappear from 

 the fecal mass. In the case of bottle-fed 

 babies, this disappearance practically coin- 

 cides with the substitution of cow's milk 

 for human milk. Cow's milk contains rela- 

 tively less sugar and more protein than 

 human milk. In either instance, the de- 

 crease of B. hifidus appears to follow very 

 closely, under normal conditions, the 

 change in diet which results in a dimin- 

 ished amount of carbohydrate in propor- 

 tion to the nitrogenous substance. That is 

 to say, as the proportion of protein in- 

 creases and the proportion of carbohydrate 

 decreases in the diet, B. hifidus also tends 

 to decrease. The decrease in the typical 

 nursling organisms is accompanied by an 

 inerease in the numbers of B. coli which 

 then dominate the intestinal tract and 

 form about 80 per cent., roughly, of the 

 total living fecal organisms of adolescence, 

 a.nd whifih persist in this proportion in 

 normal individuals until death. 



B. coli differs from B. hifidus in one note- 

 worthy respect. B. hifidus, as has been 

 pointed out before, is a strictly, almost 

 obligately, fermentative organism: it does 

 not grow in the absence of sugars. B. coli 

 is far more plastic in this respect: it can 

 grow equally well in media containing pro- 

 tein and utilizable carbohydrate, or in 

 media from which utilizable carbohydrates 

 are excluded. It can accommodate its 

 metabolism to the varying foods presented 

 to it in the intestinal contents. This plas- 

 ticity of the colon bacillus and its ability 

 to develop in the average intestinal con- 

 tents, explains in a satisfactory manner the 

 dominance of this organism throughout 

 life. 



Turning now to the distribution of bac- 

 teria in the intestinal tract of the normal 

 adults, it is found that the stomach con- 

 tents are practically sterile under normal 

 conditions. The usual explanation for this 

 sterility is the acidity of the gastric eon- 

 tents, and while this explanation may not 

 be wholly satisfactory, it suffices for the 

 moment. When the hydrochloric acid 

 acidity of the stomach contents becomes 

 diminished through disease, it is found that 

 the numbers of bacteria in the stomach eon- 

 tents may inerease greatly. The duo- 

 denum also during those periods when it is 

 empty is practically sterile. The bacterial 

 population increases as duodenal digestion 

 increases, and diminishes as the duodenal 

 contents are passed on to the lower levels. 



The greatest number of bacteria, living 

 bacteria, that is, is found in the region of 

 the ileocecal valve and the ascending 

 branch of the colon. Here the contents 

 stagnate, as it were, and they eventually 

 become so desiccated through the with- 

 drawal of water that bacterial life is re- 

 tarded. From the ascending colon pro- 

 gressively to the end of the intestinal tract 

 the number of living bacteria under ordi- 



