

PHYSIOLOGICAL CHEMISTEY. 



HISTO-CHEMISTRY. 



THE theory of the chemical nature of the animal tissues is a 

 department of physiological chemistry which as yet has been very 

 little cultivated ; and the reasons of this unsatisfactory state of our 

 knowledge are too obvious to require any detailed exposition. We 

 will, therefore, simply observe, that the most important obstacle 

 to the chemical investigation of the tissues is, that their elements 

 are too intimately combined or associated with one another to 

 admit of their being prepared for chemical analysis by a previous 

 mechanical separation. This separation of the various elementary 

 tissues which are deposited among, penetrate between, and envelope 

 one another, is rendered the more difficult by the circumstance 

 that with scarcely an exception they are equally insoluble in the 

 ordinary indifferent menstrua employed by chemists. If we have 

 recourse to the stronger or more energetic solvents, as for instance, 

 acids or alkalies, we have seldom any assurance that the dissolved 

 substance is the (otherwise) unchanged histological element, and 

 that the portion remaining undissolved is in reality a simple 

 chemically pure material ; indeed, in the majority of cases, there 

 cannot be a doubt that the chemical constitution of the tissue 

 on which we are experimenting is entirely changed by such 

 reagents. 



Various means have been attempted with the view of sub- 

 mitting the animal tissues to chemical investigation. The first 

 analyses, having any claim to accuracy, had for their object the 

 determination of the elementary composition ; in the Giessen 

 laboratory, Scherer, and subsequently others of Liebig's pupils, 

 instituted elementary analyses of several of the tissues, after purify- 

 ing them by means of the ordinary indifferent menstrua from any 

 VOL. III. B 



