THE FROG (continued) : WASTE AND REPAIR OF SUBSI 



THE DIGESTIVE ORGANS NUTRITION 



Waste and Repair. The effects of prolonged 

 cular exertion are familiar to everyone. Sooner or 

 sensations of fatigue, hunger, and thirst are proc 

 accompanied by a loss of weight. Indeed, ho 

 little exertion we make and however often we fee< 

 weight always goes down between meals and rises 

 when we take food. The loss of substance, of 

 the diminution in weight is the index, takes place 1; 

 in the form of perspiration, a fluid consisting of 

 with certain organic and inorganic matters in sol 

 A further loss is due to the air breathed out froi 

 lungs ; this is always moist, i.e., contains a good d 

 water, and is further distinguished by containing i 

 siderable volume of carbonic acid gas or carbon d 

 (CO 2 ). Besides these two constant sources of 

 there is an intermittent loss in the urine, which cc 

 of water containing certain matters in solutior 

 most characteristic of which are two complex subsl 

 called urea (CON 2 H 4 ) and uric acid (C 5 H 4 N 4 O 3 ). 

 of these, as well as carbon dioxide, act as pois< 

 allowed to remain in the system. Lastly there 

 intermittent source of loss in the waste matte 

 faeces which are passed out from the intestine. 



66 



