THE CARBOHYDRATES. 3 



physiological interest, and their chemical relationships and reactions 

 will be found described in works on chemistry. 1 



Those which are of physiological importance are the hexoses and 

 their derivatives. Nearly all the carbohydrates with which we have 

 to deal in the animal body contain either six carbon atoms, or some 

 multiple of six. The same is true of those which are used as food. The 

 remainder are either synthetical products of the chemical laboratory, or 

 more or less rare products of the vegetable world. 



But to this rule there is one exception ; the pentoses do possess some 

 physiological importance. When Hammarsten 2 was investigating the nucleo- 

 proteid material he separated from the pancreas, he found that by boiling it 

 with dilute mineral acid he obtained a reducing substance. This formation 

 of a reducing sugar-like substance from nuclein is not unique, as Kossel 3 and 

 his pupils have obtained a similar product from yeast-nuclein. The sugar, 

 however, does not ferment with yeast, but, like the pentoses, gives a red 

 coloration with phloroglucinol and hydrochloric acid, and by distillation with 

 hydrochloric acid yields furfuraldehyde. An osazone is obtainable from it 

 in the form of fine rosettes of crystals, melting at 158 to 160 C., and these 

 appear to be identical with those prepared from pentoses by E. Salkowski 

 and M. Jastrowitz. 4 



The physiological action of pentoses was investigated by W. Ebstein. 5 

 When xylose or arabinose, dissolved in water or coffee, are taken with the 

 food, they rapidly appear in the urine ; they are not assimilated. The use of 

 fruits, such as pears, that contain pentosanes, the mother substances of pentoses, 

 may lead to the appearance of the latter substances in the urine. It is 

 of course important not to confound such a temporary condition with diabetes. 



Max Cremer 6 has investigated the physiological action of some of the rare 

 sugars, especially their influence on the formation of glycogen. He found that 

 in rabbits mannose increases the hepatic glycogen, and that, though the 

 pentoses readily pass into the urine, a small quantity is assimilated as glycogen. 

 Lindeman and May 7 have confirmed Cremer's results. 



Salkowski 8 has investigated a large number of diabetic urines, but was 

 unable to find pentose in any of them. Nevertheless, he found pentose in 

 various other morbid conditions in the urine, in which their presence could 

 not be attributed to diet. He suggests that in these cases they originate in 

 the body from such nucleo-proteids as Hammarsten found in the pancreas, the 

 processes of oxidation being lessened so that they were not broken up into 

 simpler materials. 



We can now proceed to the study of the carbohydrates concerning 

 which we have more accurate physiological knowledge ; and these may 

 be classified into the following three groups : 



1 See article f: Sugars," Watts's "Dictionary of Chemistry," London, 1894, vol. iv. 



2 Ztschr.f. pliysiol. Chem., Strassburg, Bd. xix. S. 19. 



3 Kossel and Neumann, Ber. d. deutsch. chem. Gesellsch., Berlin, Bd. xxvii. S. 2215. 



4 Centralbl. f. d. med. Wissensch., Berlin, 1892. Nos. 19 and 32. Blumenthal (Berl. Urn. 

 Wchnschr., 1897, Bd. xxxiv. S. 245) has obtained pentoses from numerous other nucleo- 

 proteids. 



5 Virchows Archiv, Bde. cxxix. S. 401 ; cxxxii. S. 368 ; cxxxiv. S. 361. 



6 Ztschr.f. BioL, Miinchen, Bd. xxix. S. 484. 



7 Chem. Ccntr.-BL, Leipzig, 1896, Bd. i. S. 932. 



8 Berl. klin. Wchnschr., Bd. xxxii. S. 364. See also Kiilz and Vogel (Ztschr.f. BioL, 

 Miinchen, 1895, Bd. xxxii. S. 185). These observers found pentoses in only four out of 

 sixty-four cases of human diabetes. But they are generally found in the severe forms of 

 diabetes produced in dogs by the extirpation of the pancreas or by administration of 

 phlorid/in. 



