EXCRETION 287 



important organs for dealing with the waste products of 

 the body, and it is not surprising that extensive disease 

 of it is often associated with pronounced toxic symptoms. 

 Its reserve power, however, is so great that probably only 

 about one-fifth of its actual substance is essential for life, 

 which explains how it is that the organ may be the seat of 

 the most extensive cirrhosis without health being greatly 

 affected. 



Excretion by the Intestine. 



The intestine excretes (1) the residue of the intestinal 

 juices; (2) the unabsorbed remains of the food; (3) certain 

 mineral salts, such as calcium and iron. 



On an ordinary mixed diet the amount of faeces 

 excreted is from 120 to 150 grammes, containing 30 to 

 37 grammes of solid matter. Their composition is very 

 uniform. They are to be regarded as chiefly made up of 

 the residue of the digestive juices ; they also contain, 

 however, some starch granules, vegetable debris, and 

 a few muscle fibres derived from the food. In reaction 

 the normal faeces are neutral or slightly alkaline. The 

 alkalinity is the result of putrefaction, and is therefore 

 more pronounced if there is much protein in the diet. 



The normal colour of the stools is due in part to 

 stercobilin, but it is greatly influenced by the nature of 

 the food. Thus, if there be much meat in the diet, the 

 faeces are very dark, and if more fat be taken than can 

 be completely absorbed, they assume a clay colour. 

 Normal bile pigment (bilirubin) is never present in the 

 stools in ordinary circumstances except in early infancy, 

 but it may appear if diarrhoea be present. If the stools 



