800 PHYSIOLOGY 



about seven times as much as is contained in the urine passed in the -same 

 time. The material basis of the faeces seems to be largely desquamated 

 epithelial cells from the intestinal wall, and bacteria, of which countless 

 numbers, chiefly dead, are present. It has been reckoned that as much as 

 50 per cent, of the faeces may consist of the dead bodies of bacteria. 



Very different is the composition of faeces if the food contains a large 

 amount of cellulose. Not only does the ingested cellulose pass unchanged 

 into the faeces, but large quantities of other substances enclosed in the 

 cellulose walls may also escape digestion and absorption. Moreover the 

 increased bulk of the undigested residue stimulates peristalsis, "and thus 

 quickens the passage of the food through the gut to such an extent that the 

 digestive ferments have not time to exert their full action on the digestible 

 constituents of the food. The influence of the character of the food is well 

 illustrated by a comparison of the amount and composition of the faeces on 

 different kinds of bread (Rubner) : 



The following Table is also instructive. In this Table Rubner calculates 

 the amount of faeces which a man would pass in twenty-four hours if he 

 satisfied his energy requirements at the. expense of one only of the different 

 kinds of food enumerated. The numbers refer to the amount of organic 

 material which would be excreted in the faeces : 



Meat . . . . .26 grm. Rice ..... 50 grm. 



Eggs 26 Maize . . . 51 



Macaroni . . 27 Turnips . . 101 



Wheaten bread . . . 36 . Potatoes . . . . 133 



Milk 42 Coarse brown bread . . 146 



The indigestible cellulose in the food is not without value. It has been 

 shown previously that the peristaltic contractions of the intestine are roused 

 primarily by the mechanical stimulus of distension. If the food is capable 

 of entire digestion and absorption, the amount of faeces formed is limited 

 to that produced by the intestinal wall itself. The small bulk exercises 

 very little stimulating effect on the intestine, and the movements of the 

 latter will therefore tend to be sluggish, especially in the absence of the 

 mechanical stimulus determined by muscular exercise. The presence of a 

 certain amount of cellulose in the diet may therefore be of considerable 

 advantage by giving bulk to the faeces and ensuring the proper regular evacu- 

 ation of the lower gut. It is probable that the constipation which is so 

 common a disorder in civilised communities is due as much to the refinement 

 in the preparation of the food as to the prevalence of sedentary occupations 

 incident on the working of such communities. 



