SERIES OF VITAL FUNCTIONS. 55 



pears to have been compatible with any other imaginable 

 system. 



§ 2. Series of Vital Functions. 



In the animal economy, as in the vegetable, the vital, or 

 nutritive functions are divisible into seven kinds, namely, 

 Assimilation, Circulation, Respiration, Secretion, Excretion, 

 Absorption, and Nutrition; some of which even admit of 

 farther subdivision. This is the case more particularly 

 with the processes of assimilation, which are generally nu- 

 merous, and require a very complicated apparatus for acting 

 on the food in all the stages of its conversion into blood, a 

 fluid which, like the returning sap of plants, consists of nu- 

 triment in its completely assimilated state. It will be ne- 

 cessary, therefore, to enter into a more particular examina- 

 tion of the objects of these different processes. 



In the more perfect structures belonging to tlie higher 

 orders of animals, contrivances must be adopted, and organs 

 provided for seizing the appropriate food, and conveying it 

 to the mouth. A mechanical apparatus must there be placed 

 for effecting that minute subdivision, which is necessary to 

 prepare it for the action of the chemical agents to which it 

 is afterwards to be subjected. From the mouth, after it has 

 been sufficiently masticated, and softened by fluid secretions 

 prepared by neighbouring glands, the food must be con- 

 veyed into an interior cavity, called the Stomach,, where, 

 as in a chemical laboratory, it is made to undergo the par- 

 ticular change which results from the operation termed Di- 

 gestion. The digested food must thence be conducted into 

 other chambers, composing the intestinal tube, where it is 

 converted into Chyle, which is a milky fluid, consisting 

 wholly of nutritious matter. Vessels are then provided, 

 which, like the roots of plants, drink up this prepared fluid, 

 and convey it to other cavities, capable of imparting to it a 

 powerful impulsive force, and of distributing it through ap- 

 propriate channels of circulation, not only to the respiratory 



