THE PECULIAR FACULTIES 267 



the acts which ,make up these faculties are functions of those 

 organs. 



I shall consequently not enquire whether the functions of such 

 ■organs are being performed uninterruptedly or only intermittently, 

 nor shall I consider whether these functions subserve the preservation 

 of the individual or of the species, nor whether they act as links between 

 the individual and surrounding bodies that are foreign to it. I shall 

 merely state briefly my views on the organic functions which give rise 

 to the seven faculties named above. I shall prove that each of them 

 is limited to particular animals, and cannot be common to the entire 

 animal kingdom. 



Digestion. This is the first of the special faculties, and is possessed 

 by the greater number of animals. It is at the same time an organic 

 function carried on in a central cavity of the individual ; a cavity 

 which, although varying in shape in different races, is generally like 

 a tube or canal, which is sometimes open at one of its extremities 

 only, and sometimes at both. 



This function, which acts only on compound substances, called 

 aUmentary substances and not a part of the individual, consists firstly 

 in destroying the aggregation of the component molecules of the ali- 

 mentary substances, introduced into the digestive cavity ; and then of 

 changing the state and properties of these molecules, in such a way 

 that part of them become fitted for the formation of chyle, and for 

 renewing or restoring the essential fluid of the individual. 



Various Hquids, dehvered into the digestive organ by the excretory 

 ducts of various glands in the neighbourhood, Uquids which are chiefly 

 poured forth when digestion has to be performed, facilitate in the first 

 place the dissolution, that is to say, the destruction of the aggregation 

 of the molecules of the food substances ; and then contribute to bring- 

 ing about the changes which these molecules have to undergo. There- 

 after, such of the molecules as have been adequately altered and pre- 

 pared, are suspended in the digestive and other hquids, and penetrate 

 through the absorbent pores of the walls of the aUmentary or intestinal 

 tube into the lacteals or subordinate canals, and there constitute that 

 precious fluid which is destined to restore the essential fluid of the 

 individual. 



All the molecules or coarser parts, which are of no use for the 

 formation of chyle, are afterwards rejected from the ahmentary 

 cavity. 



Thus the special organ of digestion is the ahmentary cavity, whose 

 anterior opening by which food is introduced bears the name of mouth, 

 while that of the posterior extremity, when there is one, is called the 

 anus. 



