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PHYSIOLOGICAL CHEMISTRY 



an absolute standpoint, but relatively the percentage depends 

 upon the amount of fat. The amount in the body averages 

 also about 15%. Extractives, a heterogeneous group of com- 

 pounds classed together because they are water soluble, and 

 belong in none of the other classes, make up less than 1% 

 of the body weight. This group will receive no further treat- 

 ment as such, but the substances included in it (urea, creat- 

 inine, etc.) will be discussed individually in connection with 

 the tissues or fluids in which they occur. 



