METABOLISM 5*5 



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

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

 f)f 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 

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

 I )resence in the animal's fat of foreign fat acids such as erucic acid has 

 \ )een 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 

 S:onditions 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 

 :haracteristic of the animal, and if not immediately needed for oxidation 

 Purposes is transported to the connective tissues and deposited. Regardless 

 )f 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 

 -ransformed into fat when consumed in amounts beyond that necessary 

 IOT 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 



It was stated in a previous chapter that all the starch and sugar that are 

 consumed daily are converted by the action of the salivary, pancreatic and 



intestinal enzymes, for the most part into glucose; that after absorption the 



'glucose is transported by the blood of the portal vein to the liver; that while 

 passing through the liver capillaries, a portion passes across the capillary wall 

 into the surrounding lymph and into the liver cells in which it is dehydrated 

 by enzymic action and converted into starch (glycogen); that subsequently 



|this starch is again hydrated by the same or a different enzyme and con- 

 verted into sugar, glucose or glycose, after which it passes into the blood to 

 take the place of the sugar which has left the blood^ and which has 

 oxidized in the tissues. By this process, glycogenolysis the normal percent- 

 age of the sugar in the blood is maintained. The metabolism of the carbo- 



: hydrates in the body includes a brief statement of the formation of glycogen 

 and sugar in other tissues than the liver and more especial y in the muscles. 

 Muscle Glycogen.-Glycogen is also found in muscles and to some 

 extent in the placenta, and embryonic tissues generally. Chemic analysi 

 has shown that muscles contain from 0.5 per cent, to i per cen . and as 

 these organs amount to about 40 per cent. (28 kgm.) of weight of the body, 

 70 kgm., they generally contain from 140 to 280 grams of glycogen Inas- 

 Luch as chemic analysis has failed to demonstrate the presence of glycogen 

 in the blood, the inference is that it arises in the muscle-cell in a manner 

 similar to that observed in the liver-cell, viz.: by a transformation, through 



