84 DISACCHARIDES, POLYSACCHARIDES AND GLUCOSIDES 



striving to remedy the consequences of a totally unnecessary dietary 

 habit which arises from a threefold origin of public ignorance, a 

 fancied superiority of things which are white, and therefore "pure," 

 white bread, white eggs, white (i. e., sulphured) dried fruits, white 

 sugar (made to appear white by the addition of litmus) and so forth, 

 and in the irresponsible self-interest of millers and bakers. The War, 

 through the introduction of more thorough utilization of grains to make 

 "War flour" and "War bread" has thus no doubt proved a veritable 

 blessing in disguise to many chronic sufferers and it is not improbable 

 that the reinstatement of our former foolish and wasteful habits of 

 milling will be prevented or delayed by a more general public recog- 

 nition of the beneficial role of indigestible residues in the food. 



Cellulose occurs almost exclusively in the vegetable kingdom. It 

 is found, however, in the shells of Tunicata. Otherwise it is unknown 

 in the animal kingdom. In the cell- walls of plants, not only true cellu- 

 lose is found but other cellulose-like substances, some of which yield 

 not only glucose, but other sugars, even pentoses such as arabinose, 

 xylose, etc. Polysaccharides which yield only pentoses on hydrolysis 

 are also found, and are known as Pentosans. 



As the cell-walls of plants advance in age they undergo a peculiar 

 change resulting in the acquirement of greater rigidity. This process 

 is known as Lignification. The exact nature of the change which occurs 

 is not known, but it has been suggested that Lignin is formed from 

 cellulose by the formation of compounds with aromatic derivatives. 



The vegetable gums and mucilages are a very heterogeneous group 

 of polysaccharides. The gums are insoluble, the mucilages soluble in 

 water. The majority of them yield galactose and arabinose when hydro- 

 lyzed by dilute acids. Agar-agar, so widely used in culture-media for 

 bacteria, is a representative of this class of carbohydrates; it is derived 

 from certain marine algae. From marine algae of the Fucus type is 

 also obtained a polysaccharide yielding pentoses on hydrolysis which is 

 designated Algin. It is a colloidal substance which behaves like a weak 

 acid, forms insoluble salts of aluminium and lime, and is employed as 

 a waterproofing material and a substitute for size. 



Closely related to the gums and mucilages is a group of substances, 

 the Pectins, which are of very great industrial importance inasmuch 

 as they are responsible for the gelation of fruit-jellies. The pectins 

 are white amorphous gelatinous substances, which form colloidal solu- 

 tions in water, do not reduce Fehling's solution, and yield galactose, 

 glucose and pentoses on hydrolysis by acids. They are believed to be 

 derived by partial hydrolysis, due to the organic acids present in 

 fruit-extracts, from a series of parent-substances, the Pectoses, which 

 are present in plant-tissues in the form of insoluble calcium salts. 

 The pectins are converted by dilute alkalies or by the ferment Pectase 

 into Pectic Acid, the calcium salt of which is insoluble in water and 

 forms jellies. Since pectase is destroyed by heat, the formation of 

 fruit-jellies by extracting fruits with hot sugar-solutions is not to be 



