64 MANUAL OF PHYSIOLOGY. 



each tissue depend upon the greater development of some one of 

 these substances. 



It is of little use to classify the numerous chemical constitu- 

 ents found in the animal body, in such a systematic manner as to 

 satisfy the rules of modern chemistry, because their classification, 

 from a strictly chemical point of view, does not set forth their 

 physiological importance or express in any way the relation they 

 bear to the vital phenomena of organisms. 



The following enumeration of the chief chemical ingredients 

 found in the tissues has regard to their physiological dignity as 

 well as to their chemical construction, and will thus, it is hoped, 

 assist the student to distinguish the different groups, and give 

 him a better idea of their vital relationships, than a more strictly 

 systematic classification. 



A. NITROGENOUS. 



I. Complex bodies forming the active portions of all tis- 

 sues Plasmata. E. g., protoplasm, blood plasma. 

 II. Bodies entering into the formation of, and which can 

 easily be obtained by analysis of Group I. Albu- 

 mins. E. g., serum albumin. 



III. Bodies the outcome of differentiation, manufactured 



in the tissues by Group I. Albuminoids. E.g., gel- 

 atine, etc. 



IV. Bodies containing nitrogen, being intermediate, bye, or 



effete products of tissue manufacture. E. g., lecithin, 

 urea, etc. 



B. NON-NITROGENOUS. 



V. Carbohydrates in which the hydrogen and oxygen exist 

 in the proportion found in water. E. g., starch and 

 sugar. 

 VI. Substances containing oxygen in less proportions than 



the above. E. g., fats. 

 VII. Salts. 

 VIII. Water. 



