520 TEXT-BOOK OF PHYSIOLOGY 



two dogs were starved for a definite period. One was then- given a large 

 amount of linseed-oil and the other large amounts of mutton fat. At the 

 end of several weeks both had accumulated fat. A post-mortem examina- 

 tion of the fat of the first dog showed that it was liquid at oC. while the 

 fat of the second dog was solid at 50 C. In another experiment a dog 

 was allowed to starve until its weight had been reduced 40 per cent. It was 

 then given large amounts of fat with small amounts of meat. At the end 

 of five days, the animal was killed and found to contain 1353 grams of fat. 

 Of this amount only 131 could have come from the protein. The inference 

 therefore is that the food fat is capable of being deposited as such. The 

 presence in the animal's fat of foreign fat acids such as erucic acid has 

 been detected when the animal has been fed on colza or rape-seed oil. 



Though these facts hold true it is highly probable that under physiologic 

 conditions all the varieties of fats consumed as foods are digested and sub- 

 sequently synthesized by the epithelial cells of the villi into the form of fat 

 characteristic of the animal, and if not immediately needed for oxidation 

 purposes is transported to the connective tissues and deposited. Regardless 

 of the nature of the fat in the food, the fat of the animal is peculiar to it and 

 possesses physical and chemic properties which serve in large measure to 

 distinguish it. 



3. From Carbohydrates. That carbohydrates are capable of being 

 transformed into fat when consumed in amounts beyond those necessary 

 for heat-production is a generally well-recognized fact, though the successive 

 steps by which this is brought about have never been disclosed. It has not 

 been possible to effect this transformation by any known chemic procedure. 

 Animals fed on a diet containing the customary amounts of protein and fat 

 but containing a somewhat larger amount of carbohydrates than usual soon 

 begin to lay on fat. The many experiments on the fattening of animals have 

 placed this beyond question. This article of food must be looked on as the 

 chief source of the body fat. 



THE METABOLISM OF THE CARBOHYDRATES 



The metabolism of the carbohydrates includes a series of processes 

 that relate to their temporary storage, subsequent release and final 

 oxidation. The mechanism by which these processes are maintained 

 and coordinated is not only complicated but delicately adjusted; its 

 normal activity is very frequently disturbed by different factors with the 

 result that a portion of the ingested carbohydrates escape oxidation and 

 is eliminated in the urine constituting a condition known as glycosuria. 



The Storage of Sugar. At the outset the fact must be accepted that 

 the carbohydrates are consumed almost exclusively for the production of 

 heat and the performance of work. This fact has been established by a 

 long Aeries of experiments carried out by physiologists and chemists. 



Since the muscles are the organs chiefly concerned in the production of 

 heat as well as in the performance of work, it is a plausible assumption 

 that the storage of sugar as well as its oxidation is to be sought for in the 

 muscles themselves. As a point of departure it may be assumed that the 

 tissues have been depleted of all carbohydrate material, and that on a 

 given day the usual quantity, from 300 to 400 grams (10 to 12 ounces), 

 is consumed, digested, and converted, in the small intestine, for the most 



