POLYSACCHARIDES 83 



probable that there are many modifications of cellulose), are insoluble 

 in all ordinary solvents, such as water, alcohol, ether, and so forth. 

 Cellulose dissolves, however, in solutions of many metallic salts in the 

 presence of excess of strong acid, for example in zinc chloride in acid 

 solution, and in the hydrochloric acid solutions of antimony, mercuric, 

 or bismuth chlorides. The requisite condition for solution appears to 

 be, the presence of a salt of a weak metallic base in acid solution. 

 Another solvent for cellulose is an ammoniacal solution of cupric 

 oxide, known as " Schweitzers' Reagent." In the presence of con- 

 centrated sulphuric acid, sulphuric-acid esters of cellulose are formed 

 and pass into solution. If this solution be diluted and boiled, glucose 

 is formed and glucose only, hence cellulose is an anhydride of glucose. 

 A preliminary stage in this hydrolysis is the formation of Amyloid, 

 a soluble colloidal substance which resembles starch in yielding a blue 

 color with iodine. 



Cellulose is indigestible by any of the ferments contained in or 

 produced by mammalian tissues. It is, however, digestible by bacteria, 

 and as much as seventy per cent, of unlignified cellulose may be dis- 

 solved in vitro by the juices from the lower intestine of the horse. The 

 products of this form of digestion are not sugars, but carbon dioxide, 

 methane and fatty acids. Human beings have been found to utilize 

 as much as forty per cent, of young and tender cellulose, doubtless 

 through the agency of the intestinal bacteria. Hence the nutritive 

 value of cellulose, especially in animals such as the cow and horse 

 which possess very long intestines, is by no means negligible. But 

 the celluloses are of significance to the animal economy from yet 

 another point of view. By virtue of their incomplete digestibility 

 they communicate bulk and substance to the f eces and thus facilitate 

 their passage through the intestines, in the first place by bringing about 

 a favorable distention of the intestinal muscular walls, and in the 

 second place by furnishing these muscles with material upon which to 

 exert leverage. Prior to the introduction of "War-breads" the ten- 

 dency of our times was to eliminate indigestible carbohydrates more and 

 more thoroughly from the diet and the prevalence of intestinal stasis 

 and chronic constipation in modern communities is doubtless attri- 

 butable, in part at least, to this "refinement" of our foodstuffs. A 

 crude endeavor to correct this deficiency in our diet is frequently 

 made by mixing bran or other coarsely ground cellulose-rich materials 

 with the flour from which bread is made. This remedy may in many 

 instances, however, be worse than the disease, for the ingestion of large, 

 horny and sharp-edged indigestible fragments with the food may lead 

 to lacerations of the intestine, and consequent inflammatory reactions 

 or enteritis. What is required is finely ground cellulose-rich material, 

 such as our ancestors enjoyed when they ground up their grains by 

 hand between two hard stones. Agar is frequently employed to com- 

 municate indigestible bulk to the diet or, in recent years, heavy taste- 

 less petroleum oils, but in administering these substances we are merely 



