502 MICROBIOLOGY OF SPECIAL SIGNIFICANCE 



normally present in the faeces are produced almost altogether by multi- 

 plication within the intestine. It is nevertheless possible for swallowed 

 organisms to appear alive in the faeces even though incapable of growth 

 within the digestive tube. 



The introduction of foreign organisms capable of multiplication in 

 the gastro-intestinal canal may lead to a marked ' alteration in the 

 quantitative relationships of the faecal bacteria or even to the disappear- 

 ance of certain microbic forms previously present. Thus in cholera, 

 the vibrio of this disease may occupy the intestinal canal so completely 

 that the usual faecal bacteria can no longer be found with the micro- 

 scope. By feeding acid-resisting lactose-fermenting bacteria, such as 

 Bact.bulgaricum along with considerable quantities of milk, it is possible 

 to suppress the putrefactive anaerobes, B. edematis group, which prefer 

 a neutral or alkaline medium. The swallowed bacteria are manifestly, 

 therefore, of some importance in determining the character of the faecal 

 flora, but they are, after all, usually less important in this respect than' 

 the chemical composition of the food itself. In every case the original 

 intestinal flora has to be reckoned with as a most essential element. 



The daily excretion* of bacteria in the feces of healthy men, is, 

 on the average, about 33 million million bacterial cells. The washed 

 and dried substance of these bacteria amounts to about sJ^ g. per day. 

 From one-sixth to one-fifth of the weight of the dry faeces and probably 

 about a third of the moist faeces consists of bacterial substance. The 

 nitrogen carried away by these faecal bacteria represents a daily loss of 

 0.5 to i.o g. 



In addition to the bacteria, one often finds in the faeces yeasts and 

 protozoa. Of the latter Entamoeba coli is probably an almost constant 

 inhabitant of the intestinal tract and its numbers are often augmented 

 in mild chronic digestive disturbances. The flagellates, Lamhlia 

 intestinalis and Trichomonas intestinalis are found less frequently. 

 A few other protozoa occur in disease. 



, The physiological effects of the normal intestinal bacteria are not 

 fully understood. Some observers have maintained that continued 

 life and growth would b? impossible without the bacteria of the di- 

 gestive tract, ascribing to them an essential part in the nutrition of 

 the body. The experiments of Cohendyf seem now to have disproven 



• MacNeal, Latzer and Kerr, Jonrn, Infect. Diseases, 1909, VI, 123. 

 t Cohendy; Annales de I'institut, Pasteur, 191 i, XXVI, 106. 



