810 PHYSIOLOGY OF DIGESTION AND SECRETION. 



When kept sterile they lost steadily in weight and showed normal 

 growth only when supplied with food containing bacteria. The idea 

 that the relations between the bacteria and the animal that harbors 

 them constitutes a kind of symbiosis in which each derives a benefit 

 from the other has certainly not been demonstrated. The con- 

 trary view, that bacterial putrefaction is the occasion for constant 

 danger to the human organism, has been stated in extreme form, 

 perhaps, by Metchnikoff. According to this author the constant 

 production and absorption of bacterial toxins from the intestine is 

 one of the important causes of a loss of resistance on the part of 

 the body to the changes which bring on senescence and death. 

 At present it seems wise to take the conservative view that while 

 the presence of the bacteria confers no positive benefit, the organ- 

 ism has adapted itself under usual conditions to neutralize their 

 injurious action. 



Composition of the Feces. The feces differ widely in amount 

 and in composition with the character of the food. Upon a diet 

 composed exclusively of meats, they are small in amount and dark 

 in color; with an ordinary mixed diet the amount is increased; and 

 it is largest with an exclusively vegetable diet, especially with vege- 

 tables containing a large amount of cellulose. The average 

 weight of the feces in twenty-four hours upon a mixed diet is 

 given as 170 gms., while with a vegetable diet it may amount to as 

 much as 400 or 500 gms. The quantitative composition, therefore, 

 varies greatly with the diet. Qualitatively, we find in the feces 

 the following things: (1) Indigestible material, such as ligaments of 

 meat or cellulose from vegetables. (2) Undigested material, such as 

 fragments of meat, starch, or fats which have in some way escaped 

 digestion. Naturally, the quantity of this material present is slight 

 under normal conditions. Some fats, however, are almost always 

 found in feces, either as neutral fats or as fatty acids, and to a small 

 extent as calcium or magnesium soaps. The quantity of fat found is 

 increased by an increase of the fats in the food or by a deficient 

 secretion of bile. (3) Products of the intestinal secretions. Evi- 

 dence has accumulated in recent years* to show that the feces in 

 man on an average diet are composed in part of the unabsorbed 

 material of the intestinal secretion. The nitrogen of the feces, for- 

 merly supposed to represent only undigested food, seems rather to 

 have its origin largely in these secretions, together with the cellular 

 debris thrown off from the walls of the intestines. (4) Products of 

 bacterial decomposition. The most characteristic of these products 

 are indol and skatol. They are crystalline bodies possessing a dis- 

 agreeable, fecal odor; this is especially true of skatol, to which 



*Prausnitz, "Zeitschrift f. Biologie," 35, 335, 1897; and Tsuboi, ibid., 

 p. 68. 



