CHAPTER IX. 



INTRODUCTION. SOLVENTS. METHODS OF EXTRACTION. 

 GENERAL NOTES ON APPARATUS AND MANIPULATION. 



Introduction. 



The practical study of the transformations which 

 plastic substances undergo in metabolism is an application 

 of organic chemistry : the immediate problem is generally 

 to determine whether certain substances are present or 

 absent, and, if present, in what amounts, in particular 

 tissues. 



For the qualitative testing of insoluble substances, such 

 as proteids, starch, etc. and of soluble substances which 

 give well-marked colour reactions, such as phloroglucin, 

 inulin, etc. microchemical methods are invaluable ; but for 

 quantitative work, and often for the satisfactory identifica- 

 tion of certain compounds, it is necessary to make extracts 

 with appropriate solvents and to submit these extracts to 

 a systematic examination. 



It is the object of the physiologist to employ the 

 simplest methods which will give accurate results as 

 regards the compounds to which attention is being given, 



