GENERAL PHYSIOLOGY OF THE FROG 23 



morphoses in their life-histories, but the development is slow and gradual. From 

 what you have learned in this experiment, do you think that flies grow? Are 

 small flies the young of larger flies? 



H. SUMMARY OF PHYSIOLOGICAL PROCESSES 



1 . Food prepared in the digestive tract by the action of enzymes is absorbed 

 through the walls of the intestine into the circulatory system. 



2. Oxygen drawn into the lungs through the mechanical arrangement of the 

 respiratory system passes through the walls of the lungs or through the skin into 

 the circulatory system. 



3. The circulatory system transports food and oxygen to all parts. 



4. The living substance of the body withdraws the food and oxygen from the 

 lymph and blood, and uses them: 



a) For the formation of new chemical compounds or of new living substance 

 (process of assimilation), thus accomplishing growth. 



b) For the production of energy, by burning the food material with the aid 

 of the oxygen (process of oxidation). The living substance itself may also be 

 burned and produce energy. 



5. The waste products resulting from the oxidation are excreted into the 

 blood which carries them to the lungs, skin, and kidneys, where they are thrown 

 out from the body. The lungs excrete mainly carbon dioxide and water; the 

 skin, carbon dioxide, water, and dissolved waste matters; and the kidneys, 

 dissolved nitrogenous waste materials. 



6. The combined processes of assimilation, oxidation (or other energy- 

 producing changes), and excretion are spoken of together as metabolism. Metab- 

 olism may be denned as the sum of those chemical changes taking place in 

 protoplasm which result in the production of new compounds, new protoplasm, 

 or of energy. 



7. The energy produced in the metabolic processes is utilized to carry on 

 the activities of the body, for the contraction of muscles, conduction of nerve 

 impulses, secretion of digestive fluids, etc. 



