12 ZOOLOGY. 



Thus originates another function, the circulation of the 

 blood, and another apparatus of organs by which this is 



3 



performed. 



26. We have alluded to a kind of slow combustion which 

 takes place in the interior of animal bodies. This is effected 

 by means of the oxygen of the atmosphere which is unceas- 

 ingly absorbed by means of respiration ; and it is by the 

 same function of respiration that animals get quit of the 

 matters thus consumed. 



27. The products of the respiratory combustion, as well 

 as the matters eliminated from the tissues, and which, having 

 become as it were foreign to the economy, require to be re- 

 moved from it, give rise, by, this necessity, to a function the 

 opposite of absorption that of excretion. The character of 

 this process varies according to circumstances. It is called 

 exhalation, when the liquids escape as it were mechanically; 

 secretion, when particular liquids whose nature differs from 

 the nourishing fluid are formed by a kind of chemical 

 action. By these two ways the economy elaborates the 

 particular juices necessary for the exercise of all the func- 

 tions, whilst at the same time it expels all that is useless or 

 injurious to it. 



28. The creation of the livingmatter destined to augment 

 the mass of the tissues or to replace the parts which have 

 been destroyed, is a process or work which the physiologist 

 ought not to confound with any of the preceding phenomena ; 

 it is the act by which the organism fixes in its interior a 

 foreign matter, organizes this matter, and develops in it 

 vital properties. The function is called assimilation. 



Thus the functions of nutrition consist essentially of ab- 

 sorption, digestion, circulation, respiration, exhalation, secre- 

 tion, and assimilation. We shall now consider these great 

 acts of vegetative life. 



OF ABSOEPTION. 



29. By absorption is meant the act or faculty by which 

 animals suck up and imbibe, as it were, into the mass of their 

 humours the substances which surround them, or which are 

 deposited in the interior of their bodies. 



The existence of such a faculty may be very readily proved. 

 Plunge a frog into water, in such a way, however, that none 

 can enter by the mouth ; notwithstanding, the weight of the 



