182 ALIMENTATION. 



gard to other excretions. The quantity of the excretions is even more strik- 

 ingly modified by exercise, which, within physiological limits, increases the 

 vigor of the system, provided the increased quantity of food required be 

 supplied. 



AVhile a certain amount of waste of the system is inevitable, it is a con- 

 servative provision, that when the supply of new material is diminished, life 

 is preserved not, indeed, in all its vigor by a corresponding reduction 

 in the quantity of excretions ; and in the same way, the forces are retained 

 after complete deprivation of food much longer than if disassimilation pro- 

 ceeded always with the same activity. 



As regards the quantity of food necessary to maintain the system in 

 proper condition, it is evident that this must be greatly modified by habit, 

 climate, the condition of the muscular system, age, sex etc., as well as by 

 idiosyncrasies. 



The daily loss of substance which must be supplied by matters introduced 

 from without is very great. A large portion of this discharge takes place by 

 the lungs, and a consideration of the mode of introduction of gases to supply 

 part of this waste belongs to the subject of respiration. The most abundant 

 discharge which is compensated by absorption from the alimentary canal is 

 that of water, both in a liquid and vaporous condition. The entire quantity 

 of water daily removed from the system has been estimated at about four and 

 a half pounds (2,041 grammes), and it is probable that about the same quan- 

 tity is introduced in the form of drink and as a constituent of the so-called 

 solid articles of food. The quantity which is taken in the form of drink 

 varies with the character of the food. When the solid articles contain a 

 large proportion of water, the quantity of drink may be diminished ; and it is 

 possible, by taking a large quantity of the watery vegetables, to exist entirely 

 without drink. There is no article more frequently taken than water, merely 

 as a matter of habit, any excess being readily removed by the kidneys, skin 

 and lungs. Dalton estimates the daily quantity necessary for a full-grown, 

 healthy male, at fifty-four fluid ounces (1,530 grammes), or 3-38 pounds. 



The quantity of solid food necessary to the proper nourishment of the 

 body is shown by estimating the solid matter in the excretions ; and the 

 facts thus ascertained correspond very closely with the quantity of material 

 which the system has been found to actually demand. The estimates of 

 Payen, the quantity of carbon and of nitrogenized matter in a dry state 

 being given, are generally quoted and adopted in works on physiology. Ac- 

 cording to this observer, the following are the daily losses of the organism : 



Carbon (or its j Respiration, 8-825 oz. (250 grammes) ) ^ >10 . 941 QZ (310 grammes)> 



equivalent). ( Excretions, 2'116 oz. ( 60 grammes) ) 

 Nitrogenized substances (containing 308'64 grains, 



or 20 grammes of nitrogen) 4-586 oz. (130 grammes). 



15-527 oz. (440 grammes). 



From this he estimates that the normal ration, supposing the food to 

 consist of lean meat and bread, is as follows : 



