104 SAPROPHYTISM, PARASITISM, AND PATHOGENISM 



best known examples of obligately fermentative organisms. It does 

 not thrive on a purely protein diet but requires carbohydrate, which 

 is normally supplied by the breast milk. Breast milk, it will be remem- 

 bered, contains on the average about 7 per cent, of lactose, 3 per cent, 

 fat and but 1.5 per cent, protein. The proportion of carbohydrates 

 to protein in the diet decreases as the infant becomes older and the 

 diet becomes more liberal, and this decrease in the percentage of 

 carbohydrate is associated with a diminution in the number of the 

 obligately fermentative bacteria, particularly of Bacillus bifidus, and 

 their gradual replacement by organisms which can thrive well on a 

 diet containing variable proportions of carbohydrate and protein. 1 



Bacillus coli is a most labile organism with respect to its ability 

 to develop in the carbohydrate and protein constituents of the intes- 

 tinal contents at the ileocecal region and lower levels; this organism 

 is represented to the extent of fully 80 per cent, in the feces of healthy 

 men. Smaller numbers of other bacteria, as Micrococcus ovalis, 

 Bacillus acidophilus, B. proteus, B. mesentericus, B. aerogenes cap- 

 sulatus and many other varieties are found transiently or semi-per- 

 manently in the intestinal contents. Exogenic bacteria occasionally 

 invade the tissues of the body through the intestinal mucosa. Thus 

 typhoid, paratyphoid and dysentery bacilli and cholera vibrios may 

 produce severe infections. The tubercle bacillus may pass through 

 the apparently intact intestinal wall without leaving any evidence 

 of its passage. It is supposed that this organism penetrates the 

 intact mucosa and enters lymphatic channels suspended in fats and 

 eventually proliferates in deeper tissues. 



3. Genito-Urinary System. Vagina. The vagina has an acid reac- 

 tion and it harbors very few bacteria, but immediately afterchild- 

 birth the reaction may become temporarily alkaline. The bacillus 

 of Doderlein, however, occurs so commonly, that it may be provision- 

 ally regarded as a normal inhabitant and a few strains of aciduric 

 cocci are not infrequently detected in cultures from the fundus of the 

 vagina. The Gonococcus and Treponema pallidum are the more 

 common pathogenic organisms whose portal of entry is the vagina. 



Uterus. The normal uterus is sterile and the acid reaction of the 

 vagina and the closure of the cervix uteri tends to maintain sterility 

 under normal conditions. During menstruation and childbirth the 

 mechanical defenses of the uterus are impaired. The organ itself 

 appears to possess no specialized powers of resistance to infection. 



1 A more detailed discussion on intestinal bacteria and their significance will be found 

 in Chapter xxx. 



