358 A MANUAL OF VETERINARY PHYSIOLOGY 



with the oxygen used to oxidise the sulphur of proteins, account 

 for the deficit. 



Great interest attaches to the carbohydrates in the feeding of 

 herbivora, as so little fat exists naturally in vegetable food. 

 We have learnt that the carbohydrates are one of the sources 

 of muscular energy, and with horses they are the chief source ; 

 this material is ' fired off ' by the muscles during contrac- 

 tion ; and under the influence of muscular work and starvation 

 the whole store in the body may be used up. As the result of 

 the oxidation of carbohydrates heat is generated, so that these 

 substances supply not only energy but heat to the body. The 

 seat of the necessary oxidation is, as we have seen (p. 129), 

 in the tissues, and not in the blood ; the tissues produce enzymes 

 which break up the sugar with the formation of carbon dioxide 

 and water ; these enzymes are called into activity by the internal 

 secretion of the pancreas. The amount of heat generated by the 

 oxidation of sugar can easily be measured, 1 gramme (15 J grains) 

 yields 4,100 calories, or 4-0 large calories of heat.* Oxidations 

 are constantly going on throughout the life of the animal. During 

 rest they are providing for the internal work and heat of the 

 body, while during work, in addition to these, they furnish the 

 muscular energy. The influence of carbohydrate as a protein 

 sparer has already been mentioned ; less protein is required with 

 the food when carbohydrates are present in sufficient quantity. 

 The value of carbohydrate in the diet was first established by 

 Lawes and Gilbert, at a period when protein was considered 

 the essential basis of all dietaries. Not only did these patient 

 observers prove the absolute necessity of carbohydrates in the 

 diet of fattening animals, but they showed that weight for weight 

 the feeding value of starch and cane sugar was nearly the same. 



The Fats. — The fat of animals is a compound of glycerin and 

 fatty acids, the latter being stearic, palmitic, and oleic ; the two 

 former confer on fat its firmness, the latter enters into the for- 

 mation of the fluid fats. The melting-point of fat depends 

 upon the proportion of fatty acids in the mixture, the melting- 

 point of olein being very low, and that of stearin and palmitin 

 high. Olein is the solvent of the other fats. In milk fatty acids 

 of the volatile series are present — butyric, caproic, caprylic, etc. 

 As previously noted, there is very little fat in the food of herbi- 

 vora — in fact, the amount is so small that in the fattening of 

 animals fat is always specially added to the diet. It might hence 

 be natural to conclude that the fat in the body is derived from 

 the fat in the food, but this does not cover the whole ground ; 

 great stores of fat may exist in animals receiving a trifling amount 

 of fat in the diet : a cow, for instance, may produce more fat in 



* A large calorie is the amount of heat necessary to raise 1 kilogramme 

 (2*2 pounds) water i° C. (i*8° F.), and is conveniently named a kilo-calorie. 



