ANIMAL JUICES. 3 



readiness with which many of the constituents are decomposed, 

 but principally on the impossibility of perfectly and uniformly 

 drying large quantities. In order to avoid as much as possible 

 these and other impediments, we must only employ small quantities 

 of the object in our analysis. 



Notwithstanding every care and precaution, difficulties will 

 however present themselves in the analysis of animal substances, 

 which may escape even the closest attention ; and hence, more 

 than in the analysis of any other substances, it is absolutely 

 necessary to institute a rigid controlling comparison of the various 

 results, and even a partial repetition of them. Since the same 

 quantity of an animal fluid serves for the determination of only a 

 few of its constituents, our means of controlling the analysis are 

 increased in proportion to the number of determinations made 

 independently of each other. Thus, for instance, in seeking to 

 ascertain the amount of coagulable matters contained in a fluid, 

 the analysis should always be controlled by extracting the solid 

 residue of the fluid with alcohol, ether, and water, and then 

 comparing the quantity of the insoluble matters with the number 

 representing the protein-body determined by coagulation. Thus 

 too, ash-analyses should always be controlled by comparing the 

 mineral constituents of the individual extracts with those of the 

 collective ash. A perfect coincidence would certainly prove the 

 inaccuracy of the analysis in both these cases ; for the coagulated 

 substance, unless it has been expressly deprived of its fat, still 

 contains fat, and sometimes even other substances soluble in 

 alcohol but not in water, and which, on the other hand, cannot 

 occur in that portion of the solid residue of the fluid extracted 

 with alcohol and ether, and insoluble in water; for this must always 

 contain more earthy salts than the albumen that has been com- 

 pletely coagulated by the addition of a weak acid. In like manner 

 the analysis of the collective ash cannot coincide with that of the 

 individual extracts, since, for instance, the sulphur contained in 

 the coagulable matters is unable to exert a metamorphic action on 

 the soluble salts of the extracts, whilst the composition of the 

 combined ash must be altogether different, partly on account of 

 the sulphuric acid formed from the unoxidised sulphur of the 

 protein-bodies, partly from the difficult combustion of albuminous 

 substances, and partly from other causes. Although this method 

 may not afford any strict means of controlling these relations, it. 

 furnishes a more correct view of the true nature of the substances 

 dissolved in the fluid. This is, to a certain degree, a physiological 



B 2 



