204 



from no other source than through the organs of 

 digestion and secretion can it be conceived to be de- 

 rived. But our knowledge of the theory of these 

 functions in animals, as in vegetables, is extremely 

 limited and imperfect : and while it so continues, no 

 rational explanation of this matter can be expected 



or obtained. 



* 



161. Nearly the same remarks maybe made con- 

 cerning the primary and original source of carbon in 

 the superior animals. To the organs of digestion, 

 assimilation, and secretion alone, are we enabled to 

 trace it ; but the mode in which it is reduced to that 

 state in which it is afterwards expelled by the surfa- 

 ces of the lungs and skin, involves a knowledge of 

 the nature and qualities of our food, of the various 

 and successive changes which it is made to undergo 

 in the system, and of its distribution by the blood to 

 the different organs of secretion, according to the se- 

 veral uses which it is afterwards destined to answer : 

 concerning all of which subjects, we have of late 

 succeeded in getting rid of much error and absurdi- 

 ty, but have not, in any instance, attained to com* 

 plete knowledge. 



