360 



SCIENCE 



[N. S. Vol,. XLII. No. 1080 



is not surprising to find, therefore, that as the 

 breast-fed infant becomes older and its dietary de- 

 mands more varied, B. iifidus tends to disappear 

 from the fecal mass. In the case of bottle-fed 

 babies, this disappearance practically coincides 

 with the substitution of cow's milk for human 

 milk. The decrease in the typical nursling organ- 

 isms is accompanied by an increase 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, and which 

 persist in this proportion in normal individuals 

 until death. 



B. coli differs from B. iifidus in one noteworthy 

 respect. B. coli can grow equally well in media 

 containing protein 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 plasticity of the colon bacillus and 

 its ability to develop in the average intestinal con- 

 tents, explains in a satisfactory manner the domi- 

 nance of this organism throughout life. 



Turning now to the distribution of bacteria in 

 the intestinal tract of the normal adult, it is found 

 that the stomach contents are practically sterile 

 under normal conditions. When the hydrochloric 

 acid acidity of the stomach contents becomes 

 diminished through disease, it is found that the 

 numbers of bacteria in the stomach contents may 

 increase greatly. The duodenum also during those 

 periods when it is empty is practically sterile. 

 The bacteria population increases as duodenal di- 

 gestion increases, and diminishes as the duodenal 

 contents are passed on to the lower levels. 



The greatest number of living bacteria is found 

 in the region of the ileocecal valve and the ascend- 

 ing branch of the colon. Here the contents stag- 

 nate, as it were, and they eventually become so 

 desiccated through the withdrawal of water that 

 bacterial life is retarded. 



The significance of the intestinal flora has been 

 variously interpreted. Nuttall and Thierfelder 

 delivered guinea-pigs by CEesarean section and 

 attempted to raise them in a sterile environment 

 on sterile food. For two weeks these sterile guinea- 

 pigs increased in weight and appeared to be rea- 

 sonably healthy. These observers drew the con- 

 clusion that the intestinal bacteria were not neces- 

 sary for the well-being of these guinea-pigs at 

 lea^t. These experiments were not accepted by 

 Schottelius as being conclusive. He claimed that 

 the experiments were not carried on long enough. 

 Schottelius experimented with chicks hatched from 



sterile eggs divided into three groups. These 

 were incubated under sterile conditions, and the 

 chicks developing from one group were kept in an 

 absolutely sterile environment and fed on sterile 

 food; a second group were kept under the same 

 conditions for ten days and then fed with in- 

 fected food; the third group were controls and 

 were kept under ordinary conditions. The first 

 group, the sterile chicks, did well for ten days, but 

 after that time their development was seriously re- 

 tarded. The second group also did well for ten 

 days, and then, as the first group began to exhibit 

 signs of abnormalities, they were placed on in- 

 fected food: they gained rapidly. The third 

 group, kept under ordinary conditions, did well 

 from the start. Schottelius believed that his ex- 

 periments showed that the intestinal bacteria were 

 necessary for the development and well-being of 

 chicks. 



Madame Metehnikoff made similar observa- 

 tions on tadpoles, and Moro performed the same 

 experiments with turtles. These observers agree 

 with Schottelius that the intestinal flora appear to 

 be necessary for the well-being of the animals they 

 experimented on. 



A line of evidence which is somewhat different 

 from this was brought forward by Levin. He ex- 

 amined the fecal contents of many Arctic mammals 

 in the Arctic regions, and he found few or no bac- 

 teria in them. 



Attempts have been made to sterilize the intes- 

 tinal contents of man, either by administering ster- 

 ile food or by the use of antiseptics, but this line 

 of experimentation has not been successful. 



From the individual point of view the intestinal 

 flora under ordinary conditions are innocuous, and 

 perhaps even to a moderate degree protective. But 

 under abnormal conditions, when progressively 

 pathogenic bacteria gain a foothold in the intestinal 

 tract, the intestinal flora may become a menace to 

 health and may become a matter of real concern 

 to the health of communities. 

 The General Mechanism of the Action of Fer- 

 ments — Enzyme Action: C. S. Hudson". 

 A discussion of the chemical changes involved 

 in the action of enzymes. 

 Use of Bacteria in the Treatment of Textile 



Fibers: F. P. Gorham. 

 Microorganisms in Their Application to Agricul- 

 ture: 0. E. Marshall. 



Professor Marshall's complete paper has been 

 published in. Science. 



A. Paekek Hitchens, 



