PROTEIN-COMPOUNDS. 327 



of solving this question will be made apparent on comparing the 

 properties of these substances, and considering the observations 

 already made (at pp. 29-30) on the determination of the atomic 

 weights. It must rather excite our surprise that chemists should 

 have hazarded any theory of their composition, than that nothing 

 positive should as yet have been ascertained regarding their com- 

 position and mutual relations. Although we have the most accu- 

 rate analyses of the protein-compounds, it is impossible to form 

 any decisive conclusion regarding their internal constitution ; for 

 although the exactness of Mulder's analyses is undoubted, their 

 accuracy must yet be only commensurate with the present com- 

 paratively imperfect state of analytical chemistry; that is to say, the 

 empirical results of the analyses of these bodies do not admit of 

 our deciding with scientific certainty on their composition. Hence 

 a formula deduced from these analyses must be simply hypothe- 

 tical, since several formulae may frequently be derived with equal 

 correctness from one and the same analysis. In making choice of 

 one of these formulas we must therefore adopt that which appears 

 to guide us in the best direction, bearing in mind that we have to 

 deal with hypotheses only, and not with facts. 



Keeping this consideration in view, we have, in the following 

 remarks, adhered to Mulder's recent hypothesis, in accordance with 

 which albuminous substances are regarded as combinations of a 

 purely hypothetical substance, incapable of being exhibited in an 

 isolated form, with different quantities of sulphamide and phospha- 

 mide. We only follow this hypothesis, because from the want of a 

 safer guide, it seems the best adapted to lead us in our advance 

 through this obscure department. 



The following properties are common to all the protein-com- 

 pounds. Most of them occur in two conditions, namely in a soluble 

 and in an insoluble or scarcely soluble state ; in the former condition, 

 we find them naturally existing in the animal fluids, while they are 

 principally obtained in the latter form by boiling. The soluble 

 modification forms in a dry condition a faint yellow, translucent, 

 friable mass, having no smell or peculiar taste ; it dissolves in water, 

 but is insoluble in alcohol and ether; it is precipitated by alcohol from 

 the aqueous solution, after which it is usually insoluble in water ; 

 the aqueous solution may have either a slightly alkaline or a slightly 

 acid reaction, which depends, however, more on the alkali or acid 

 mixed with it than on the substance itself. The aqueous solution 

 is precipitated by most metallic salts, and the precipitate generally 

 contains the acid and base of the salt employed in addition to the 



