326 PROTEIN-COMPOUNDS. 



enable us to establish a purely chemical basis on which to ground 

 their arrangement. But physiology so far aids us, that it indicates 

 which of these substances are to be regarded as original and pro- 

 togenic in the animal body, and which are to be regarded as origi- 

 nating from these by a zoo-chemical process, and constituting their 

 derivatives. The protogens or aborigines of these substances, 

 which are, in part, found in the embryo, bear so striking a 

 resemblance to one another, that chemists have discovered only very 

 slight, fluctuating, and often merely relative differences between 

 them. We cannot wonder, therefore, that chemists should have 

 conjectured that these, which had previously been termed albu- 

 minous bodies, possessed one common radical. 



Mulder believed that he had discovered this radical, which, from 

 its great importance, he designated as protein, whilst he regarded 

 the ordinary albuminous substances as combinations of this protein 

 with sulphur and phosphorus, or simply with sulphur, and there- 

 fore called them protein-compounds. Although great doubt has 

 recently been thrown on Mulder's view of protein and its com- 

 pounds, we yet retain these names for the sake of facilitating our 

 comprehension and general examination of these combinations. We 

 purpose considering the protein-compounds or albuminous bodies 

 in the first group of histogenetic substances. As, however, phy- 

 siological chemistry has shown, with great appearance of proba- 

 bility, that all other nitrogenous animal substances are derived 

 from these protein-compounds, we will comprise, under the second 

 group, all those more generally diffused substances of the animal 

 body, which may be regarded as proximate or remote derivatives 

 of these compounds. 



PROTEIN-COMPOUNDS. 



The bodies belonging to this group occur not only in animals, 

 but also to a certain extent in plants. They were for a long time 

 regarded as merely different isomeric modifications of one and the 

 same compound ; but subsequently, as already observed, they have 

 been considered by Mulder to be combinations of one and the 

 same atomic group with sulphur and phosphorus. The difficulty 



