GLUCOSIDES 89 



Crustacea. It may be obtained in colorless semi-transparent lamellae 

 which are stained reddish-brown by iodine; on addition of sulphuric 

 acid or zinc chloride the color changes to blue or violet. Hydrolysis 

 with strong acids yields about seventy-five per cent, of d-glucosamin. 

 Chitin also contains acetyl radicals which are liberated as acetic acid 

 on fusion with alkali. 



Prolonged treatment with alkali in the cold leads to the formation 

 of " soluble chitin" which is diffusible through parchment, but has an 

 extraordinary affinity for water, carrying the water in the dialyzer 

 with it as it traverses the parchment, and withholding it from the 

 cavity of the dialyzer against hydrostatic pressure. Other products 

 of the partial hydrolysis of chitin are crystallizable (chitosans). 



GLUCOSIDES. 



The glucosides are a large and important class of substances, occur- 

 ring in great variety in certain vegetable tissues, and also in exceedingly 

 important tissues and localities in the animal body. They yield 

 monosaccharides on hydrolysis and other radicals which differ widely 

 in different glucosides. 



Reference has already been made to the glucoside Amygdalin which 

 occurs in the kernels of cherries and almonds and is hydrolyzed by the 

 ferment Emulsin, yielding glucose, hydrocyanic acid and benzaldehyde. 

 Various species of the Cruciferce contain irritant glucosides, notable 

 among which are Sinigrin or Potassium Myronate in the oil of black 

 mustard, obtained from the seeds of Sinapis nigra, and Sinalbin, in 

 the oil of white mustard, obtained from the seeds of Sinapis alba. 

 Both sinigrin and sinalbin are hydrolyzed in the presence of water by a 

 ferment, Myrosin, which occurs in the tissues of the plants from which 

 they are obtained. The products yielded by the two glucosides are, 

 however, very different, sinigrin yielding dextrose, potassium bisul- 

 phate, and allyl isosulphocyanate, while sinalbin yields dextrose, sinapin 

 sulphate (a sulphate of an alkaloid) and methyl phenyl isosulpho- 

 cyanate. Both glucosides are intensely irritant when applied to the 

 skin, and are utilized for this purpose in therapeutics. 



Glucosides of great therapeutic importance are also found in the 

 leaves and seeds of Digitalis purpurea, Strophanthus and Scilla, and 

 comprise the most important active constituents of the pharmacopceial 

 preparations made from these plants. They have a characteristic 

 action upon heart-muscle of which advantage is taken in the medical 

 treatment of cardiac affections. The same plants also contain gluco- 

 sides which are either without effect upon the heart, or else have an 

 effect which is of secondary importance. Some of these glucosides are 

 members of the saponin series and contribute to the effectiveness of 

 aqueous extracts of the plants by holding in solution substances which 

 would otherwise be insoluble in water. 



