PHYSIOLOGICAL CHEMISTRY, 



ANIMAL JUICES. 



IN our methodological introduction ' to physiological chemistry, 

 (see vol. i. pp. 12 14), the position was indicated which the 

 theory of animal juices occupies, as an intermediate link between 

 the theory of the organic substrata and that of the zoo-chemical 

 processes; while the point of view was likewise defined from which 

 this branch of physiological chemistry ought to be considered. 

 It therefore only remains for us to make a few remarks on the 

 mode of arrangement adopted in the following chapters, before 

 proceeding to the special consideration of our subject. We purpose 

 following in the main the same mode of arrangement which we 

 endeavoured to pursue in treating of the organic substrata in the 

 first volume ; that is to say, we shall begin the notice of each 

 object by considering its physical and chemical characters. The 

 mode of preparation seems at first sight a matter of little moment, 

 since these substances are usually submitted to examination 

 in the condition in which they are directly yielded by nature. 

 But although the exhibition of such objects does not require the 

 aid of chemistry, we may often find it difficult to command the 

 mechanical and physiological means requisite for procuring the 

 substance in a pure condition, that is to say, unmixed and unde- 

 composed. The result of the whole chemical operation is often 

 dependent on the manner in which the object is exhibited, and it 

 will be found that an unsuitable method of exhibition frequently 

 leads to the adoption of wholly erroneous views in reference to the 

 nature and function of an animal fluid. It is only when we are 

 convinced that the animal fluid is presented to us in the same 

 state in which it exists in the living body, that we can hope to 

 obtain any physiological result from our investigation. As the 

 exhibition of many animal fluids, moreover, frequently requires that 



VOL. II. B 



