12 METHODOLOGICAL INTRODUCTION. 



demonstrate its presence in the animal juices and tissues. The 

 qualitative analysis of organic bodies is still far behind that of 

 inorganic bodies, but attention to this point is the more necessary, 

 since deficient investigations too often lead to hasty and erroneous 

 opinions. Nor does less importance attach to a correct estimate of 

 the methods that have been employed for the quantitative determi- 

 nation of the main constituents of animal fluids ; for it is only by 

 this means that we can form an opinion of the value of many of 

 the existing quantitative analyses of physiological and pathological 

 products, and of the conclusions which we are justified in deducing 

 from them. 



The physiological consideration of every substance must of 

 necessity be primarily based on its mode of occurrence, for we 

 cannot form any opinion of the importance of a body in reference 

 to the changes of animal matter without knowing where, in what 

 relations, and in what quantity it occurs. When, however, we have 

 examined the origin and decomposition of a substance, we have 

 obtained the firmest base for the explanation of the vital chemical 

 processes. 



After having, in this manner, familiarised ourselves with the 

 organic substrata of the animal body, we are still only on the 

 threshold of the study of the constitution and functions of the 

 animal juices and tissues. Before, therefore, we proceed to the 

 actual study of physiological chemistry, (namely, the theory of the 

 metamorphosis of matter, or of the zoo-chemical processes,) we 

 take into consideration the substances with which we have already 

 become acquainted in zoo-chemistry, regarding them topographi- 

 cally, in reference to their simultaneous occurence,[and their blend- 

 ing and admixture under the form of animal juices, tissues, and 

 organs. We may extend this classification to the animal fluids as 

 well as to the tissues and entire organs. No one will deny that 

 the knowledge of the chemical constitution of these more complex 

 and frequently variable parts of the animal body is another basis 

 of physiological chemistry, for it is evident that if we would treat of 

 chemical processes, we ought to have a knowledge of the sub- 

 stances implicated in them. This however, cannot yet be attained 

 in zoo-chemistry in the sense that we attach to this science. We 

 here enter the domain of physiology, in as far as we submit the 

 direct results of physiological actions to an investigation, which how- 

 ever must still be of a purely chemical and essentially analytical 

 character. 



The province of chemistry in the consideration of the animal 



