56 APPLIED BIOLOGY 



53. Nutrition. Fundamental Processes. We have now 

 briefly traced food from its entrance into the frog's body 

 through the changes of digestion, absorption, and distribution 

 to the living cells. These cells are active living machines re- 

 quiring food (1) for repairing their waste and for growth, 

 and (2) for oxidizing to give the energy which is expended 

 in the activities of the body. Sooner or later most of the 

 materials entering the cells as food become combined with 

 oxygen, and the resulting substances are excretions of no 

 further use to the living cells. 



All the changes which food and oxygen undergo, beginning 

 with their reception into the body and ending with. their 

 elimination in the form of excretions, involve the processes 

 of digestion, absorption, circulation, respiration, changes 

 within cells (metabolism), and excretion. It is important to 

 remember that all these processes are fundamental, for one 

 is just as necessary as another. All the processes taking 

 of food, digesting of food, its absorption by the blood, its 

 transportation to the cells, its absorption by the cells, its 

 use by the cells, the supplying of oxygen, and the removal 

 of excretions all these processes are linked together, as 

 it were, in a chain, and each process must play its part in 

 the life of the body. 



54. Need of Organs Working Together : Coordination. 

 All the organs concerned in the processes named in the 

 paragraph above must work together, for if any organ fails 

 in the proper performance of its work, the result is that the 

 working of all the organs of the body is affected. For ex- 

 ample, if the heart beats slower, the blood flows slower, 

 and consequently the supply of food and oxygen to the cells 

 and the removal of excretions will be lessened. We know that 

 if the heart stops beating, or the lungs cease acting, animals 

 die at once ; and the reason is that the cells of the body 

 fail to get their necessary food and oxygen and the poisonous 

 excretions are allowed to accumulate. We see then how 



