232 A Manual of Veterinary Physiology. 



for the purpose of comparison ; the case must therefore be 

 regarded as exceptional. 



In starvation about 90 to 100 per cent, of the fat dis- 

 appears, and the muscles lose from 60 to 70 per cent, in weight. 



Muscular Exertion. — The chief cause of body-waste is 

 work. There are other and smaller causes, but this is 

 obviously the most important. The performance of mus- 

 cular work increases the action of the heart, lungs, muscles, 

 skin, etc. Potential energy is converted into heat and 

 work, and this is produced by the oxidation of food into 

 its decomposition products. 



The changes in the tissue resulting in heat and motion 

 occur almost entirely, if not exclusively, amongst the non- 

 nitrogenous elements. This has been settled beyond all 

 doubt. It is not the nitrogenous substances, as we might 

 suppose, considering their essential nature, which lead to 

 heat and motion ; and the urea of the urine does not con- 

 sequently represent a measure of the work performed. 

 Heat and motion are exclusively the function of the non- 

 nitrogenous food. This is a curious fact, ami apparently 

 plunges us into the difficulty of explaining why an animal 

 cannot live, let alone work, without receiving proteids, and 

 that the heavier the work performed the more proteid re- 

 quired. The explanation is that the absorption of oxygen, 

 without which no oxidation of the non-nitrogenous elements 

 can occur, is dependent on the amount of proteid taken in. 



Amount of Food required.— Muntz (quoted by Colin), from 

 his investigations into the food required by the Paris 

 omnibus-horses, came to the conclusion that, five- twelfths 

 of the total ration was expended on internal work and 

 repair, and seven-twelfths on muscular work ; and he showed 

 that a horse performing 9 to 10 miles per diem required for 

 1,000 lbs. of body-weight: , b 



Nitrogenous matter - - 2*83 



Fatty matter - "75 



Non-nitrogenous extractives 17*00 



( 'ellulose ami lignin - - t> '-'i> 



On this diet they neither lost nor made flesh. 



