V OF 



'vLlFUMN! A. 



CHAPTER I. 



THE PROTEIDS. 



AMONGST the organic proximate principles which enter into the 

 composition of the tissues and organs of living beings, those belonging 

 to the class of proteid or albuminous bodies occupy quite a peculiar 

 place and require an exceptional treatment, for they alone are never 

 absent from the active living cells, which we recognize as the primor- 

 dial structures of animal and vegetable organisms. In the plant, 

 whilst we recognize the wide distiibution of such constituents as 

 cellulose and chlorophyl, and acknowledge their remarkable physio- 

 logical importance, we at the same time are forced to admit that 

 they occupy altogether a different position from that of the proteids 

 of the protoplasm out of which they were evolved. We may have a 

 plant without chlorophyl and a vegetable cell without a cellulose 

 wall, but our very conception of a living, functionally active, cell, 

 whether vegetable or animal, is necessarily associated with the 

 integrity of its protoplasm, of which the invariable organic constitu- 

 ents are proteids. 



In the animal, the proteids claim even more strikingly our 

 attention than in the vegetable, in that they form a very much larger 

 proportion of the whole organism, and of each of its tissues and organs. 

 We may indeed say that the material substratum of the animal 

 organism is proteid, and that it is through the agency of structures 

 essentially proteid in nature that the chemical and mechanical 

 processes of the body are effected. It is true that the proteids are 

 not the only organic constituents of the tissues and organs, and 

 that there are others, present in minute quantities, which probably 

 are almost as widely distributed, such as for instance phosphorus- 

 containing fatty bodies, and glycogen, yet avowedly we can (at the 

 most) only say probably, and cannot, in reference to these, affirm 

 that which we may confidently affirm of the proteids that they are 

 indispensable constituents of every living, active, animal tissue, and 

 indissolubly connected with every manifestation of animal activity. 



There are then, it will be admitted, good reasons why a general 

 sketch of the proteid bodies should be the proper introduction to a 

 treatise on physiological chemistry, in which the classification is 



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