THE MUTUAL RELATIONS. 315 



administered as much as 350 grams per day. The animal under experi- 

 ment, a dog, weighed 15 kilograms. If, in accordance with common 

 experience, we assume that this animal had stored up 11 grams of glycogen 

 per kilogram of weight, at the beginning of the experiment, we obtain, as 

 the total amount of glycogen present, 165 grams, corresponding to 183 

 grams sugar. If we take the maximum value, 40 grams of glycogen 

 per kilogram weight, we have 600 grams glycogen, corresponding to 664 

 grams sugar. 1 The animal under experiment, however, excreted 1408.4 

 grams sugar. With the first assumption, 1225 grams, and with the 

 second, 744 grams, of sugar thus remain unaccounted for. The ingested 

 albumin and glycerol must be regarded as producing this sugar. The 

 animal excreted 209.8 grams nitrogen during the whole period of the 

 experiment. Liithje calculated that, at most, 630 grams of sugar could 

 have been produced from the conversion of the albumin. This leaves 

 considerable sugar still unaccounted for unless we admit that it came from 

 the glycerol. Liithje's experiment is the only one which really proves 

 that glycerol can be converted into sugar. 2 All of the other investigations, 

 namely, those which showed an increase in the glycogen content of the 

 liver, are not above criticism. The discovery that the animal cell is 

 capable of transforming glycerol into sugar is another connecting link 

 between the animal and plant cells. We must not, however, deceive 

 ourselves with the thought that the conversion of glycerol into sugar takes 

 place in normal metabolism to any considerable extent. We know it is 

 true that fats, before being absorbed, are more or less disintegrated into 

 their components, glycerol and fatty acids. We also know that neutral 

 fats are formed again in the intestine. A small amount of free fatty acids 

 remains, and likewise some glycerol. There is but very little, however. 

 It might be possible for fat to undergo combustion without previous 

 hydrolysis, and the glycerol therein converted into glucose instead of being 

 consumed with the rest of the fat molecule. The amount of such glycerol 

 would be only 11 per cent of the neutral fat, and this is relatively little. 



The next question that arises is whether the fat itself, i.e., the fatty 

 acid component also, can go over into sugar. Direct experiment indicates 

 that this is not the case. Fat itself does not cause any increase of sugar 

 in the urine, even in the most severe cases of diabetes. E. Pfluger, who 

 has recently come to the conclusion that a source of sugar other than the 

 carbohydrates' themselves must be looked for in bad cases of glucosuria 

 and diabetes, nevertheless holds to the opinion that fat can produce sugar. 

 He explains the fact that fat does not cause any increased excretion of 



1 E. Pfliiger calculates as a maximum 615 grams sugar. (See Glycogen, loc. cit. p. 537.) 



2 More recently Karl Griibe, Pliiger's Arch. 118, 1 (1907), has shown that glycerol 

 after having been passed through the liver of a turtle caused an increase in the 

 glycogen content of this organ. 



