THEORY OF "WASTING." 433 



the question we are at present considering. We may accept 

 the truth of the statement, that the quantity of food or drink 

 which eVery fat person consumes, is too large in proportion 

 to the amount of exercise he takes. If this were not so, 

 we would have instances of under-fed and hard-worked horses 

 being too plump ! It is almost needless to say that their 

 nutrition is regulated in a manner similar to that of mankind. 

 On the other hand, there are both men and horses that no 

 amount of good food and idleness could make obese ; because 

 their organs of assimilation are abnormally inactive. 



THEORY OF "WASTING." 



The human body is a motor machine in which movement 

 is produced and heat maintained by the oxidation of its 

 structures (tissues) ; the oxygen for this purpose being 

 absorbed into the body from the air taken into the lungs. 

 As far as the production of heat is concerned, this oxidation 

 is similar to the combustion of wood or coal in a fire ; but 

 the production of motion appears to be more or less a direct 

 result of oxidation without the intermediate stage of heat, 

 which we see in a steam engine. The principal products of 

 the union of the tissues with oxygen are carbonic acid, water, 

 and waste nitrogenous matter. In addition to the loss of 

 substance from the continued process of oxidation, the 

 weight of the body is further reduced by the escape of 

 water which is passed out of the system in an unchanged 

 condition. Carbonic acid gas is given off by the lungs and 

 to a slight extent by the skin ; and water is removed by 

 the skin, lungs and kidneys. The excretion of waste nitro- 

 genous matter is a more complex affair. Under conditions of 

 health, almost all of this debris is removed from the tissues, 

 by the blood, in the harmless form of urea, which is very 

 soluble in water, and which is carried out of the body in a 

 dissolved state in the urine. In health, a small percentage of 



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