THE BACTERIA OF THE HUMAN BODY 331 



useful to the human body. Fischer says that the fresh human 

 faeces contain 75 per cent water and i per cent bacteria. 



The intestinal tract of the infant at birth is sterile, but in a 

 very short period of time after birth (i 2 to 1 8 hours) , before any 

 nutriment has been taken, bacteria appear in the meconium, 

 and as soon as milk is ingested they increase rapidly in numbers. 

 Seven different species of bacteria have been isolated from 

 the intestine of the infant before any nutriment has been 

 taken. These bacteria probably come from the air. B. 

 coli and Bact. acidi-lactici are some of the first organisms to 

 be noted in the intestine, and the former usually remains an 

 inhabitant of the intestinal tract throughout life. 



It has been shown by careful experiments, after removing 

 a guinea pig fcetus from the pregnant mother by Caeserian 

 section under strict aseptic precautions, feeding the young 

 animal with sterilized food, and using every means to prevent 

 contamination, that, after eight days, when the animal was 

 killed, the intestine was sterile. The 'experiment serves to 

 illustrate that bacteria have little or nothing to do with in- 

 testinal digestion at this period at least, and that they are 

 not present in the intestines at birth. 



The saprophytic bacteria in the normal intestinal tract are 

 absolutely harmless as long as the mucous membrane which 



lines the canal is uninjured. If this be injured, some of the 



p 



bacteria may enter into the tissues and produce serious dis- 

 eased conditions. They may accomplish this alone or in con- 

 nection with some of the pathogenic species which occasion- 



