THE MUTUAL RELATIONS. 323 



than following solely the elimination of sugar, would more likely lead to 

 a solution of the problem. 1 



In this connection, the question arises whether all carbohydrates are 

 able to form glycogen. We have already seen that glucose and fruc- 

 tose are glycogen-formers. We also know that milk-sugar and cane- 

 sugar, 2 on being introduced into the blood, are eliminated unchanged in 

 the urine. Cane-sugar is normally disintegrated in the intestine. The 

 usefulness of milk-sugar is evidently dependent on the presence of lactase, 

 as E. Weinland 3 has shown. Glycogen does not seem to be formed from 

 pentoses. 4 There is a large amount of uncertainty concerning these ex- 

 periments on account of the fact that a compound which causes an accu- 

 mulation of glycogen, need not necessarily itself participate in its pro- 

 duction. The combustion of the substance may indirectly shield, for 

 example, glucose from oxidation, thus causing deposition of glycogen. 

 Although this objection may seem uncalled for, there is much in its- 

 favor. Perhaps only those sugars are glycogen-formers which are capable 

 of going over into glucose; for grape-sugar is, probably, the only building 

 material of glycogen. All of those compounds which can be changed 

 into it, must be looked upon as producers of glycogen. 



We now reach the problem as to the relations of albumins to fats. Is 

 albumin converted into fat? There is, a priori, no reason why such a 

 change should be impossible. We know that the nitrogen in urea only 

 carries with it a part of the carbon present in the albumin, while the larger 

 part of the carbon in albumin is transformed in the body in some other 

 way. It is conceivable that these other carbon chains may be deposited 

 in the form of fat under certain conditions, in which case a direct fat 

 accumulation might result from a diet of albumin. The assumption of 

 the formation of fats from albumin would be of considerable value with 

 reference to the production of sugar from albumin or fat, for those inter- 

 mediate compounds which lead to the synthesis of fat from albumin may 

 also be closely related to the formation of sugar. We should, as a rule, be 

 rather cautious in assuming such complicated changes, especially in view 

 of the rapid progress of albumin metabolism. On the other hand, the old 

 ban, which was so long placed on the animal cell as not being in any man- 

 ner capable of effecting a synthesis, will gradually have to be withdrawn. 

 It is desirable, therefore, to establish more proof from other points of view. 



1 One might expect the problem to be solved by following the respiratory exchange. 

 Unfortunately there are no convincing investigations at hand. Cf. E. Pfliiger: Pfliiger's 

 Arch. 108, 473 (1905); Magnus Levy: Z. klin. Med. 56, 83 (1905). 



2 F. Voit: Deut. Arch. klin. Med. 58, 523 (1897). 



3 E. Weinland: Z. Biol. 38, 16 and 606 (1899); 40, 386 (1900). Cf. also R. H. A. 

 Plirnmer: J. Physiol. 34, 93 (1906). 



4 E. Salkowski: Z. med. Wiss. 11 (1893). Z. physiol. Chem. 32, 393 (1901). 



