3,52 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



in Vbit's experiments. The result of this criticism has been to make us more 

 cautious in attributing the origin of body-fat solely or mainly to proteids, hut 

 as regards the possibility of some proteid being converted into fat in the body 



there can be do reasonable doubt. It has been proved (p. 328) that glycogen 

 may be formed from proteid, and since it is now generally accepted that fats 

 are formed from carbohydrates, the possibility of an indirect production of fats 

 from proteid- seems to follow necessarily. 



The connection between the carbohydrates of the food and the fat of the 

 body has been a subject of discussion and investigation anions: physiologists 

 for a number of years. It was the original belief of Liebig that carbohydrates 

 are the source of body-fat. This view was afterward abandoned under the 

 influence of the work of Pettenkofer and Voit, but renewed investigations seem 

 to have re-established it upon -olid experimental grounds. In some older 

 experiments of Lawes and Gilbert it was shown that the fat laid on by a young 

 pig during a certain period was greater than could be accounted for by the 

 total fat in the food during that period, plus the theoretical maximum obtain- 

 able from the proteid fed during the same time. Of more recent experiments 

 demonstrating the same point, a single example may be quoted from Rubiier. 1 

 a- follow-: A small dog, weighing 6.2 kilograms, was fed richly with meat for 

 two davs and was then starved for two days ; its weight at the end of this time 

 was 5.89 kilograms. The animal was then given for two days a diet of cane- 

 sugar 100 grams, starch 85 grams, and fat 4.7 grams. It was kept in a respira- 

 tion apparatus and its total excretion of nitrogen and carbon was determined : 



Total C excretion 87.10 grams C. 



" C ingesta 176.fi " " 



89.5 " " retained in the body. 



flu- total nitrogen excreted = 2.55 grams. The carbon contained in the pro- 

 teid thus broken down plus that in the 4.7 grams of fat = 13 grams. If we 

 make the assumption that all of the C from these two sources was retained 

 within the body, there would still be a balance of 76.5 grams C (89.5 — 13.0) 

 which must have been stored in the body either as glycogen or as fat. The 

 greatest possible storage of glycogen was estimated at 78 grams = 34.6 grams 

 C, so that 76.5 — 34.6 = 41.9 grams C as the minimal amount which must 

 have been retained as fat and must have arisen from the carbohydrates of the 

 food. Similar experiments have been made upon herbivorous animals, and 

 as the result of investigations of this character we are compelled to admit that 

 the carbohydrates form one source, and possibly the main source, from which 

 the body-fats arc derived. This belief accords with the well-known fact that 

 in fattening stock the best diet is one containing a large amount of carbo- 

 hydrate together with a certain quantity of proteid. On the view that fats 

 were formed only from proteids, the efficacy of the carbohydrates in such a diet 

 was supposed to lie in the fact that they protected a part of the proteid from 

 oxidation, and thus permitted the formation offal from proteid; but it is now 

 believed that the carbohydrates of a fattening diet are, in part, converted 

 1 Zeitschrift fiir Biologie, 1SS6, Bd. 22, 8. 272. 



