104 PRINCIPLES OF PHYSIOLOGY 



production of leucocytes. Finally, matters 

 that are undigested ; chemical substances 

 arising from proteins that have not been 

 absorbed; special matters secreted by the 

 glands of the great intestine of which we know 

 little ; countless bacteria ; and earthy matters, 

 such as phosphates of lime and magnesia, 

 are voided in the faeces, 



55 There are several interesting questions 

 as to absorption that must be noticed, as an 

 answer to them takes us to first principles. 

 Water and soluble salts are absorbed un- 

 changed. The salts may be adsorbed. Carbo- 

 hydrates are all absorbed as sugars, and 

 they are carried to the liver and are there 

 transformed into glycogen (a kind of animal 

 starchy substance), and stored for a time 

 No doubt some may pass along in the 

 blood stream, and be at once used by the 

 tissues. It is highly probable that when 

 no fresh sugar is coming from the intestine 

 sugar is supplied from the liver to the 

 tissues, that is to say glycogen is changed 

 by a liver enzyme into sugar, and this is at 

 once washed away. There are good grounds 



