282 Mary Davies Swartz, 



Ebstein (109), Frantze (111), Neuberg and Wohlgemuth (128), Sal- 

 kowski (137), V. Jacksch (117),Lindemann and May (122),Brasch (96) 

 and others, that the pentoses and methyl-pentoses (rhamnose) are ex- 

 creted more readily than the hexoses; that they exert an unfavorable 

 effect in diabetes; and that there is no evidence of their acting as gly- 

 cogen-formers in man. Consequently, even if further experiments 

 justify Konig and Reinhardt's conclusions, the pentosans must appar- 

 ently still play a very small part in the nutrition of man. 



Occurrence and Nature of Galactans. 



Next to the pentosans, no hemicelluloses seem to be so widely dis- 

 tributed as the galactans; both occur together in the plant cell, and 

 often in a more or less intimate chemical combination. The pure 

 galactans, i.e., those yielding exclusively galactose upon hydrolysis, 

 have been differentiated into several classes, chiefly by differences in 

 s )lubility or specific rotation, namely: 



1. a-galactan, so named by Miintz (199), the first to identify 

 galactan as an anhydride of galactose; it composes 42 per cent of 

 luzerne seeds and occurs also in beans, barley, and malt. 



2. |3-galactan, isolated from the lime residues in the sugar beet 

 industry by Lippmann (192). 



3. 7-galactan, first isolated from Chinese moss {Sphaerococcus 

 lichenoides) by Payen (262), in 1859, and by him called "gelose." 

 He also identified it in agar-agar^ {Gelidium corneum) and other algae. 

 The carbohydrates of agar-agar were again studied by Reichardt in 

 1876, who obtained a substance of the formula C12H22OU and con- 

 sidered it identical with the "pararabin" which he found in carrots 

 and beets.2 In 1881 and 1882, Greenish (180, 181) investigated the 

 carbohydrates of Fucus amylaceus (Ceylon agar-agar) and obtained 

 on hydrolysis a sugar-yielding mucic acid (galactose) . From Sphaero- 

 coccus: lichenoides he also obtained a substance resembling Payen's 

 "gelose." In 1884, Bauer (169) showed that agar-agar yields galac- 

 tose; and in 1905, Konig and Bettels (190) gave the following per- 

 centage composition of Japanese agar-agar from Gelidium: 



Per cent. Per cent- 



Galactans $$ Ash 3.5 



Water 20 Pentosans 3.1 



Protein 2.6 Crude fiber 0.4 



'The term agar-agar is appHed to the hot water extract of various red algae, 

 mainly species of Gelidium. 

 ^See Pentosans, p. 268. 



