110 LECTURE VI. 



sion by another method. They determined the amounts of excreted 

 products from a dog, which had been given a liberal fat diet, with but 

 little meat. They found that all the nitrogen appeared again in the excre- 

 tions, but that all the carbon did not do so. I. Munk 1 could also obtain 

 storage of fat in a starved dog, by fats, or even fatty acids. 



The proof that nutrient fat and stored-up fat possess direct inter- 

 relations, has also been obtained in still another manner. For fourteen 

 days I. Munk 1 fed a dog, weighing 16 kilograms after nineteen days' fasting, 

 on fatty acids obtained from mutton-tallow. The weight of the animal, 

 which had been reduced 32 per cent during the previous fasting period, 

 then showed an increase of 17 per cent. On dissecting the animal, a very 

 large fat addition was noted. On " trying out" this, about 1100 grams 

 of fat were obtained, which was solid at room temperature, and melted at 

 40 C. It is well known that mutton-tallow melts at this temperature, 

 while fat from a normal dog would possess a far lower melting-point 

 (about 20 C.). I. Munk used rape-seed oil in a second experiment. A fat 

 was obtained which melted at 23 C. while at 14 C. a granular crystalline 

 deposit separated. The fat obtained showed 82 . 4 per cent oleic acid, and 

 12.3 per cent fatty acids. Normal dog-fat contains only 63.8 per cent 

 oleic acid, and 28.8 per cent solid acids. Rape-seed oil contains erucic 

 acid (C22H4 2 O 2 ). This was isolated from the above dog-fat. 



It is very remarkable, that a food-stuff, and especially a vegetable one, 

 should determine the composition of an animal tissue. We shall see later, 

 that the decomposition of the organic food-stuffs not only makes it 

 possible for them to be absorbed, but also enables the organism to select 

 the material necessary for its own development. 2 In fact, the fatty tissues, 

 together with glycogen, maintain a distinct individuality when compared 

 with the other substances of the tissues. Both are reserve-materials 

 which the organism stores up, in order to utilize them when needed. We 

 do not, however, desire to place glycogen and fat in the same category. 

 Glycogen is of far more importance in metabolism, than is fat in the true 

 fatty tissues. It is continually being used up in metabolism, and also 

 being constantly redeposited. The fat supplies in the liver, and possibly in 

 other organs also, act similarly to glycogen. They likewise undergo quick 

 changes. The fatty-tissue proper, however, is a true tissue under ordinary 

 circumstances. Aside from its function as a reserve material it serves for 

 other purposes, e.g., a purely mechanical one (like the fat in the eye-socket, 

 etc.), and again as a non-conductor of heat. It must not be inferred that 

 the fat is. deposited as a dead mass entirely protected from metabolism. 



1 Arch. f. (Anat. u.) Physiol. 1883, 273; Virchow's Arch. 95, 407 (1884). Cf. G. 

 Rosenfeld: Verb. d. 17, Kong. f. in. Med. 503 (1899). 



2 Cf. E. Abderhalden: Zentr. Stoffwechsel- Verdauungskrankheiten, 5, No. 24, 647 

 (1904). 



