656 DIABETES 



ance will not occur in a simple alkaline peroxide solution it 

 may nevertheless be effected by the addition of a second catalyst, 

 and still we know that the lactic acid was not an intermediate in 

 the original solution until the oxygen supply became deficient. Lactic 

 acid is probably an intermediate in the sugar cataboHsm only during 

 relative asphyxia. 



All the substances whose formulae are given above have been shown 

 to be capable of conversion into glucose in the body. The details 

 of the steps involved have not been established, but, in conformity 

 with the chemical theories developed by Nef and discussed under 

 hexoses, the transformation of these substances into glucose, as well 

 as their occurrence in the course of its breakdown, are best explained 

 on the basis that all of them participate in the same great chemical 

 equilibrium with the sugars, and that this participation depends upon 

 their dissociation into unsaturated residues. These residues are in 

 dynamic chemical equilibrium with the molecules from which they 

 are derived and with those derived from sugars. When there is a 

 rapid loss of glucose from the body these substances tend to become 

 glucose, in accordance with the laws of chemical equilibrium. 



TETROSES 



There are six possible tetroses (4 aldo- and 2 keto-). The entire subject of 

 their physiology, which has undoubtedly considerable biologic importance, has 

 been little studied. They have never been found in the urine, since there are at 

 present no established methods for their detection, and efforts have been lacking. 



PENTOSES 



Chemical theory demands the existence of fourteen pentoses, i. e., six aldo- 

 pentoses, four 2-keto-pentoses and four 3-keto-pentoses. Only those better 

 known to chemists have received biological study, e. g., arabinose and xylose.^* 

 Of these the optically inactive or d- 1-arabinose, the 1-arabinose and 1-xylose are 

 the best known. When even small quantities of pentose gain access to the cir- 

 culating blood, pentose is excreted in the urine. Ebstein^^ reports the appearance 

 of traces in the urine of a man (in which none had been previously demonstrated), 

 after the administration of so little as 0.25 gram of 1-arabinose by mouth. Ber- 

 gelP" found reactions for pentose in the urine seven to ten minutes after ingestion 

 of the same sugar, and when given subcutaneously. Fr. Voit^^ saw about 50 per 

 cent, excreted. Neuberg and Wohlgemuth" gave a normal man 15 grams of d- 

 1-arabinose and recovered 4.5 grams of d-, and only 1.04 grams of 1-arabinose in 

 the urine. On the other hand 1-arabinose becomes converted in part into the 

 dextro-form, since both forms appear in the urine when only one is given. Xylose 

 has been found to behave in general like arabinose.-' 



Since all writers agree that 10 to 50 per cent, of administered pentoses are 

 excreted in the urine even when given per os in very small quantities, and since 

 pentoses occur in many foods (plums, cherries, apples, etc.) or result from the 



'* Rhamnose is a methyl pentose, representing a class of substances closely 

 related to the jjentoscs. 



'» Virchow's Archiv., 1892 (129), 401. 



i"" Festschr. f. E. v. Leyden, 1902 (2), 401. 



2' Dcut. Arch. f. klin. Med., 1897 (58), 523. 



" Zeit. f. physiol. Chem., 1902 (35), 41. 



" For literature, see Neuberg, " Der llaru sowie die iibrigen Aussclieiduiigen, 

 etc." (Springer, Berlin, 1911), 1, p. 370. 



