130 PHYSIOLOGY. 



that it may occur but once in several days. The stools are then 

 small in amount and dark in color. The stimulating action of vege- 

 tables is what makes them so valuable in mixed diets, though they 

 are inferior in nutritive value, bulk for bulk. 



Although the faeces are so variable quantitatively, they are more 

 consistent qualitatively, and present the following substances: 



I. Water. In health about 75 per cent.; this becomes much 

 greater during diarrhoea. 



II. Indigestible Residue of different foodstuffs, as nuclein, kera- 

 tin, from epidermic structures, haematin from haemoglobin, ligaments 

 of meat, cellulose from vegetables, mucin, wood-fibers, gums, resins, 

 and cholesterin. 



III. Undigested Food. The quantity of food ingested has an 

 effect. The more one eats, the more likely he is to have a quantity 

 of undigested matters in the stool. These undissolved substances 

 ere usually pieces of vegetables, muscle-fibers, connective tissue, and 

 small quantities of casein and fat. These materials help to accelerate 

 peristalsis and so interfere with a proper absorption of those foods 

 that would otherwise be readily taken up. 



IV. Mucous Epithelial Cells. The microscope shows these are 

 present from the intestinal surface. 



V. Derivatives of Bile-salts and Bile-pigments. These are sterco- 

 bilin, cholesterin, traces of bile-acids, and lecithin. 



VI. Number of Putrid Products, as skatol, indol, phenol, volatile 

 fatty acids, ammonia, sulphuretted hydrogen, and methane. 



VII. Inorganic Salts.' These are salts of sodium, potassium, cal- 

 cium, magnesium, and iron. 



VIII. Micro-organisms.- Bacteria of numerous kinds are present 

 in the faeces. 



The coloring matter is stercobilin. The odor is due to skatol 

 an'd indol. 



The faeces in part are a product of secretion of the intestine 

 itself. Hence the nitrogen of the faeces comes not only from indi- 

 gestible food, but also from the secretion of the intestine, and thus 

 is a partial index of metabolism. 



The Color depends upon the kind of food ingested; meat gives 

 dark-brown or black, vegetables light-yellow, faeces. The reaction 

 is normally alkaline in adults, while in infants it may be acid and 

 yet not pathological. 



Meconium is the name given to the greenish-black contents of 

 the large intestine of the foetus which is expelled at or after birth. 



