THE GENERAL ANIMAL FUNCTIONS 87 



115. Summary. 



1. Division of labor and differentiation of structure proceed 

 together as the individual develops. All tissues retain the 

 power of using food, of oxidation, of eliminating useless prod- 

 ucts. Other functions incidental to these may be relegated to 

 special cells or tissues. 



2. Associations of tissues to accomplish a more or less definite 

 work are called organs. Organs of a similar kind are collectively 

 known as systems of organs. 



3. The principal functions of animals and the organs or 

 systems performing the work may be classed as follows: 



Function System 



(a) Metabolism Nutritive. 



(6) Support and protection. . . Skeletal, and integumentary. 



(c) Growth 



(d) Reproduction Reproductive. 



(e) Motion Muscular, in connection with 



skeletal. 



(/) Sensation Nervous, including sensory epi- 

 thelium. 



4. Metabolism or nutrition embraces the following processes: 

 (a) Ingestion of food (including oxygen), 



(6) Digestion, 



(c) Absorption (from the digestive tract, and at every other 

 cell wall), 



(d) Circulation, 



(e) Assimilation = anabolism, 



(/) Dissimilation = katabolism (including respiration), 

 (g) Secretion and excretion (of waste matter including carbon 

 dioxid). 



The processes in (a), (b), (c), and (e) are anabolic, i.e., add 

 to the resources of the body. Those in (/) and (g) are katabolic, 

 i.e., tend to destroy the materials, develop energy, and eliminate 

 waste. Circulation contributes to the accomplishment of both 

 purposes. 



5. The supportive skeletal structures may be internal, or 

 external, or both. They may arise as a secretion of the super- 



