28 ORGANIC SUBSTRATA OF THE ANIMAL ORGANISM. 



duly considered, we ought not wholly to lose sight of the physio- 

 logical relations of individual substances. It is not enough to 

 describe the properties, composition, preparation, and decomposi- 

 tion of matters without also considering their physiological cha- 

 racter. The occurrence of a substance in certain parts of the animal 

 body and in certain processes, its relation to the general metamor- 

 phosis of matter, and its progressive or regressive formation, 

 are all questions for whose solution we do not look to pure che- 

 mistry, although physiology alone is equally incompetent to the 

 task. 



A structure such as we have endeavoured to sketch, appears to 

 us indispensable to zoo-chemistry, before we can expect that 

 physiology and medicine will furnish an exact reply to those 

 general questions in chemistry which refer to the more important 

 processes. Similar views have undoubtedly guided most true 

 natural enquirers in their labours in this field of scientific investi- 

 gation. Nor have such men as Berzelius, Wohler, Liebig, and 

 Mulder, ever undertaken investigations which from their deficiency 

 in all scientific bases could not lead to any scientifically reliable 

 results. We find that such men have always endeavoured to afford 

 that internal scientific support to pure zoo-chemistry without which 

 it must continue a mere medley composed of disjointed facts. In 

 the present day we are, however, justified in expecting well- 

 grounded physiological results from pure zoo-chemistry, nor do 

 we exaggerate in stating that more light has been thrown on the 

 metamorphosis of animal matter by such zoo-chemical investiga- 

 tions, as Mulder's on albuminous substances, Liebig's on creatin, 

 and Wohler's on uric acid, than by many hundred analyses of the 

 blood and urine. 



In accordance with the views already advanced, we shall in 

 the following sketch of the zoo-chemical elements, retain those 

 groups that have been established by the most recent investiga- 

 tions of pure chemistry. Bodies of homologous chemical value 

 must also possess common physiological relations. We shall begin 

 with bodies of the simplest composition, most of which have seldom, 

 if ever, been found developed in the animal organism ; but with 

 which it is necessary we should become acquainted as the derivatives 

 of animal substances. By thus passing from the groups of simply 

 constituted bodies to those of more complicated composition, we 

 shall gradually become more familiar with the mechanism of the 

 association and separation of organic matter, until we are finally 

 enabled to form a correct judgment of the most complicated sub-* 



