HEAT SUPPLY. 43 



and that the former cannot be replaced altogether by the 

 latter. The horse, it appears, is far more independent of a 

 supply of fat in his diet, than is man ; but whether it 

 can be dispensed with altogether or not, is a question I 

 am unable to answer. The fact, however, of a certain, 

 though varying proportion of fat, in the natural food of 

 the animal, indicates, I think, its value, if not its absolute 

 necessity. In the daily diet, given by Dr. Parkes, for a 

 man performing very laborious work, we find that the 

 fat is to the starch and sugar, as one is to four ; while the 

 proportion for a horse, on a full supply of oats and hay, 

 is about one to sixty. 



In equine food, it appears that sugar may be entirely 

 replaced by starch, though the converse of this does not 

 hold good. 



Heat Supply. The constant oxidation of carbon and 

 hydrogen attended by the formation of carbonic acid 

 and water in the various tissues, is attended by the 

 evolution of heat, which serves to sustain the internal 

 temperature of the body at about 99' 5 p F. During 

 exercise, there is a proportionate increase in the amount of 

 tissue broken up by these chemical combinations taking 

 place, but the greater portion of the excess of heat, ap- 

 pears to be utilized by its becoming converted into 

 motion ; for we find that after rapid movement, which is 

 necessarily accompanied by considerable waste of tissue, 

 there is but a very slight increase to the temperature 

 of the body. This is in accordance with the generally 

 accepted view, that heat is an allotropic form of motion. 



Mineral Substances. These, with the exception of 

 common salt, are obtained in ample sufficiency from the 



