OBJECTS.] INTRODUCTORY. 87 



the same proportions. Indeed, charcoal, which is 

 impure carbon, might be obtained by strongly heating 

 either a handful of corn, or a piece of fowl's flesh, in 

 a vessel from which the air is excluded so as to keep 

 the corn or the flesh from burning. And if the vessel 

 were a still, so that the products of this destructive 

 distillation, as it is called, could be condensed and 

 collected, we should find water and ammonia, in some 

 shape or other, in the receiver. Now ammonia is a 

 compound of the elementary bodies, nitrogen and 

 hydrogen ; therefore ( 50) both nitrogen and hydrc- 

 gen must have been contained in the bodies from 

 which it is derived. 



It is certain, then, that very similar nitrogenous com- 

 pounds form a large part of the bodies of both the 

 wheat plant and the fowl, and these bodies are called 

 proteids. 



59. Proteid Substances are met with in 

 Nature only in Animals and Plants; and 

 Animals and Plants always contain Pro- 

 teids. 



It is a very remarkable fact that not only are such 

 substances as albumin, gluten, fibrin and syntonin, 

 known exclusively as products of animal and vegetable 

 bodies; but that every animal and every plant, at all 

 periods of its existence, contains one or other of them, 

 though, in other respects, the composition of living 

 bodies may vary indefinitely. Thus, some plants con- 

 lain neither starch nor cellulose, while these substances 

 are found in some animals ; while many animals contain 

 no horny matter and no gelatin-yielding substance. 

 So that the matter which appears to be the essential 



