NITROGENOUS HISTOGENETIC SUBSTANCES. 321 



Albuminate of soda, fibrin itself, and Mulder's protein-oxides, 

 cannot assuredly be regarded in the light of excrementitious sub- 

 stances, but must rather be considered to constitute the transitions 

 from albuminous to gelatigenous substances. 



When we reflect that the different stages of metamorphosis of 

 such non-nitrogenous bodies as the fats and carbo-hydrates increase 

 the number of the extractive matters, it seems worthy of notice 

 that their sum in the blood should not be greater than we generally 

 find it to be. But this circumstance proves that very small quan- 

 tities of the substances which must necessarily occur in the blood, 

 appear simultaneously ; and hence the difficulties of the inquiry 

 are considerably increased. The reasons why we are thus unfortu- 

 nately constrained to continue the use of the term extractive matters, 

 are sufficiently clear, but yet we cannot refrain from expressing 

 our surprise that, considering the present condition of our science 

 in this respect, chemists can venture to speak of different erases 

 of the blood, or attempt to make them serve as the foundation of 

 a presumed exact humoral pathology. 



NITROGENOUS HISTOGENETIC SUBSTANCES. 



The substances belonging to this class present, like the fats 

 and carbo-hydrates, such great similarities in their composition, 

 and in their most essential properties, that chemists, even if they 

 were unacquainted with their occurrence in the animal body, and 

 with their great physiological importance, would naturally have 

 placed them in one group, seeing that the following properties are 

 common to all of them. 



In the dried state they occur in a solid mass, or in powder, 

 or form gelatinous, brittle, translucent plates; when moist they are 

 either translucent and yellowish, opaque and white, solid and 

 elastic, soft, tough, and adhesive, or, finally, jelly-like and slippery. 

 All these substances are uncrystallisable, and, unless when an in- 

 termixture of other substances is present, are devoid of taste and 

 smell. By far the greater number of them are insoluble in water, 



