DIGESTION A SPECIAL FUNCTION. 225 



digestive act which takes place in an alimentary canal, 

 by means of secretions capable of cheinically modifymg 

 the food, so as to prepare it for Assimilation. 



The preparation of food we have seen to be both 

 mechanical and chemical, but I select the latter as the 

 specific characteristic of the digestive process, in order 

 to prevent confusion. Claude Bernard says : " We can 

 conceive an animal without any digestive apparatus, me- 

 chanical or chemical, because living in an element which 

 furnishes nutritive material directly ; we can also con- 

 ceive the digestive act reduced to a simple mechanical 

 apparatus, which has to press out certain alimentary 

 juices capable of nourishing the tissues tuithout under- 

 going chemical modifications ; but usually the diges- 

 tive act is composed of two orders of phenomena, phy- 

 sical and chemical/''' This is a brief and luminous 

 classification as regards the whole animal series, and 

 it well expresses the ascending complexity of that 

 series ; but inasmuch as special functions only make 

 their appearance at certain stages of that ascending 

 series, inasmuch as the simpler animals have not the 

 special functions of more complex animals, we must 

 deny to the two first classes of M. Bernard's series 

 any such special function as Digestion, and confine 

 it to the third class. We do not, except in loose lati- 

 tude of phrase, speak of the legs of an animalcule, 

 meaning its organs of Progression ; because, a leg is a 

 specific organ of Progression, uniform in its elements 

 throughout the series of animals possessing legs ; nor 



* Claude Bernard : Legons de Physiol. Experimentale, ii. 490. 



P 



