^o PHYSIOLOGICAL CHEMISTRY 



stannous chloride and zinc bromide. In hydrochloric acid solution the solvent action 

 of the above salts is increased. The following salts are also good solvents in hydro- 

 chloric acid solution: mercuric chloride, bismuth chloride, antimony pentachloride> 

 tin telrachloride and titanium tetrachloride. In the case of the last-mentioned salt 

 the swollen, transparent character of the cellulose fibers preliminary to solution 

 can be seen very nicely. 



Try selected solvents suggested by the instructor. 



HEMICELLULOSES 



The hemicelluloses differ from cellulose in that they may be hydro- 

 lyzed upon boiling with dilute mineral acids. They differ from other 

 polysaccharides in not being readily digested by amylases. Hemi- 

 cellulose may yield pentosans, or hexosans upon hydrolysis. 



Pentosans. Pentosans yield pentoses upon hydrolysis. So far as is 

 known they do not occur in the animal kingdom. They have, however, 

 a very wide distribution in the vegetable kingdom, being present 

 in leaves, roots, seeds and stems of all forms of plants, many times in 

 intimate association or even chemical combination with galactans. In 

 herbivora, pentosans are 40-80 per cent utilized. 1 The few tests on 

 record as to the pentosan utilization by man 2 indicate that 80-95 

 per cent disappear from the intestine. According to Cramer, 3 bacteria 

 are efficient hemicellulose transformers. It has not yet been dem- 

 onstrated that pentosans form glycogen in man, and for this reason 

 they must be considered as playing an unimportant part in human 

 nutrition. Gum arabic an important pentosan may be hydrolyzed 

 by concentrated hydrochloric acid if boiled for a short time. The 

 pentose arabinose results from such hydrolysis. 



Galactans. In common with the pentosans the galactans have a very 

 wide distribution in the vegetable kingdom. The pure galactans yield 

 galactose upon hydrolysis. One of the most important members of 

 the galactan group is agar-agar, a product prepared from certain types 

 of Asiatic sea- weed. This galactan is about 50 per cent utilizable by 

 herbivora 4 and 8-27 per cent utilizable by man. 5 Agar ingestion has 

 been shown to be a very efficient therapeutic aid in cases of chronic 

 constipation. 6 ' 7 This is particularly true when the constipation is due 

 to the formation of dry, hard, fecal masses (scybala) , a type of fecal 

 formation which frequently follows the ingestion of a diet which is 



1 Swartz: Transactions of the Connecticut Academy of Arts and Sciences, 16, 247, 1911. 



2 Konig and Reinhardt: Zeit.f. Untersuchung der Nahrungs u. Genussmittel, 5, no, 1902. 



3 Cramer: Inaug. Diss., Halle, 1910. 



4 Lohrisch: Zeit.f. exper. Path. u. Pharm., 5, 478, 1908. 



5 Saiki: Jour. Biol. Ghent., 2, 251, 1906. 



6 Mendel: Zentralblat f. d. gesammte Phys. u. Path, des Sto/w., No. 17, i, 1908. 



7 Schmidt: Munch, med. Woch., 52, 1970, 1905. 



