NUTRITION 359 



her milk than she receives in her food ; a pig lays up more than 

 exists in the fat plus protein contained in the diet ; so that it 

 is evident a something not fat can furnish it. This something is 

 the carbohydrate which when in excess of requirements is stored 

 up as fat in the permanent fat-reserve depots of the body, and 

 subsequently doled out to the system as required. Perhaps 

 also the non-nitrogenous portion of the protein molecule may 

 contribute to fat formation, though this point is not settled. 

 The storing up of fat is a physiological process, but under certain 

 circumstances it may constitute a pathological condition. By 

 its oxidation, which is referred to more fully at p. 364, fat fur- 

 nishes heat and energy, and in this respect is of higher value 

 than an equal quantity of carbohydrate ; 1 gramme (15 J grains) 

 of fat yields 9-3 large calories on oxidation. How it is prepared 

 for oxidation is unknown ; the fat as it lies in masses in the body 

 cannot be oxidised until it is brought back into the blood and 

 carried to the tissues, and it is suggested that the fat-splitting 

 ferment, lipase, decomposes the fats into fatty acids and glycerin, 

 in much the same way that the same ferment splits the fat in the 

 intestinal canal before absorption. Should this be the case, the 

 lipase regulates the supply of fat to the blood. It has been 

 stated that in the blood the fat derived from the intestines on 

 absorption is changed into an unknown substance, which is 

 soluble, easily reversible, filtrable, dialysable, and so transported 

 into the tissues.* It is, therefore, assumed that what applies to 

 fat when taken up from the intestines holds good for that taken 

 up from the body. 



There are certain fat-reserve depots natural to the animal, 

 and on which, under ordinary circumstances, little or no drain 

 occurs ; such are found beneath the peritoneum, around the 

 kidneys, in the mesh of the omenta, and surrounding the base 

 of the heart. It is only under the influence of starvation that the 

 fat in these places is drawn on. The chief means to induce the 

 laying on of fat is a liberal diet and freedom from exercise and 

 work. The farmer feeding for beef or mutton understands the 

 value of keeping the animals as quiet as possible, and recognises 

 also that there are certain breeds which have a distinct pre- 

 disposition to store up fat. Further, he learns how necessary 

 it is to introduce animals gradually to a fattening diet until 

 toleration is established, and he knows from practical experience 

 that he will not succeed in fattening within a reasonable time 

 unless to the diet of carbohydrate and fat he also adds proteins 

 liberally. The measure of the diet is that of the animals' appe- 

 tite ; they can never eat enough to please the feeder, who cheer- 

 fully accepts the heavy initial outlay, as he knows the subsequent 



* ' Recent Advances in Physiology and Biological Chemistry.' Edited 

 by L. Hill, M.B., F.R.S. 



