90 DISACCHARIDES, POLYSACCHARIDES AND GLUCOSIDES 



From a biochemical point of view, and in our present state of knowl- 

 edge, perhaps the most noteworthy glucosides which occur in plant- 

 tissues are the various members of the Saponin and Sapotoxin group of 

 glucosides These substances are found in a very great variety of plant- 

 tissues, but especially in Quillaja, (soapbark), Saponaria (soapwort), 

 Cyclamen (cyclamin), Solatium (nightshade and potato) and Smilax 

 (sarsaparilla). These glucosides behave like weak acids and are split 

 on hydrolysis with acids into sugars and other substances which are for 

 the most part, as yet undefined. They possess to a very remarkable 

 degree the property of reducing the surface-tension at surfaces in con- 

 tact with water in which they are dissolved and coating these surfaces 

 with an insoluble film, with the result that the forces tending to cause 

 coalescence of bubbles are very much reduced, so that the water con- 

 taining saponins form froths like soap-solutions, when it is shaken up 

 with air. Hence the names "soapbark," " soapwort," etc. For the 

 same reason they have the property of holding otherwise insoluble 

 substances in solution or suspension, since the suspended particles 

 have less tendency than usual to clump together and thus form masses 

 large enough to fall out of the solution. 



The saponins and solanins readily dissolve or form colloidal solutions 

 of a variety of fatty substances, particularly the Lecithins, an important 

 group of phosphorus-containing fatty substances which will fall under 

 discussion repeatedly in future chapters. They also form, in many 

 cases, insoluble compounds with Cholesterol, an aromatic alcohol, which 

 is found associated with lecithins in all living tissues. 



The power of the saponins to dissolve fatty substances is undoubtedly 

 the origin of their remarkable action upon red-blood corpuscles, the 

 stroma of erythrocytes being very rich in lecithins and other fatty 

 substances. As little as one part of cyclamin added to 100,000 parts 

 of blood causes complete liquefaction or Hemolysis of the stroma of 

 the corpuscles with resultant setting free of the enclosed hemoglobin, 

 while liquefaction of a proportion of the corpuscles is brought about by 

 even smaller amounts. Cholesterol tends to prevent this action of the 

 saponins by combining with them to form insoluble compounds, and 

 hence blood serum or plasma, since it contains a small amount of 

 cholesterol, to some extent inhibits the hemolytic action of the saponins. 



A saponin, digitonin, which occurs in Digitalis but is devoid of 

 action upon the heart, is employed in the quantitative estimation of 

 cholesterol. 



In animal tissues glucosides are found especially among the decom- 

 position-products of Nucleic Acids and in the tissues of the brain. 

 The nucleic acids will fall under special consideration in a later chapter 

 and it need merely be stated here, in passing, that they are phosphoric 

 acid compounds of glucosides, the Nucleosides, which yield either 

 d-glucose or d-ribose and nitrogenous bases on hydrolysis. A nucleo- 

 side is also found in minute traces in the blood and exerts an action 

 upon the egg-cells of the Sea-urchin (Strongylocentrotus) similar to that 



