VI ECONOMY OF A MIXED DIET 275 



all food, and since it contains carbon as well as nitrogen it 

 may suffice, under certain circumstances, to maintain the 

 body ; but it is a very disadvantageous and uneconomical 

 food-stuff when taken by itself. 



Albumin, which may be taken as a type of the proteins, 

 contains about 53 parts of carbon and 15 of nitrogen in 

 100 parts. If a man were to be fed on white of egg, 

 therefore, he would take in, speaking roughly, 3^ parts of 

 carbon for every part of nitrogen. 



But we have seen that a healthy, full-grown man, 

 keeping up his weight and heat, and taking a fair amount 

 of exercise, eliminates per diem 270 to 300 grammes of 

 carbon to only 20 grammes of nitrogen, or, roughly, only 

 needs one-thirteenth to one-fifteenth as much nitrogen as 

 carbon. However, if he is to get his 270 grammes of 

 carbon out of albumin, he must eat 500 grammes of that 

 substance. But 500 grammes of albumin contain 75 

 grammes of nitrogen, or nearly four times as much as he 

 wants. 



To put the case in another way, it takes about four 

 pounds (1,800 grammes) of fatless meat (which generally 

 contains about one-fourth its weight of dry solid proteins) 

 to yield the necessary amount of carbon, whereas one 

 pound (453 grammes) will furnish all the nitrogen that is 

 required. 



Thus a man confined to a purely protein diet must eat 

 an excessive quantity of it in order to obtain the amount 

 of carbon he requires. This not only involves a great 

 amount of physiological labour in comminuting the food, 

 and a great expenditure of power and time in dissolving 

 and absorbing it, but throws a great quantity of wholly 

 profitless labour upon those excretory organs, which have 

 to get rid of the nitrogenous matter, three-fourths of 

 which, as we have seen, is superfluous. 



Unproductive labour is as much to be avoided in phy- 

 siological as in political economy ; and it is quite possible 

 that an animal fed with perfectly nutritious protein matter 



T 2 



