82 



THE CHEMICAL CONSTITUENTS OF THE BODY 



2. Gums are amorphous, transparent, tasteless and odorless substances which 

 with cold water form viscous fluids. They are very widely distributed in the 

 plant kingdom. 



(a) Among the gums the dextrins claim our chief interest here, for they are 

 formed as intermediate products in the transformation of starch in the alimen- 

 tary canal. They are obtained also by heating starch up to 200-210 C. In 

 these transformations of starch a series of dextrins is formed which have smaller 

 and smaller molecular weights. The dextrins are white or yellowish white, amor- 

 phous, gumlike masses whose aqueous solutions are dextro-rotatory. They are 

 not directly fermentable. 



(Z>) An animal gum is said to be split off from mucin through the influence of 

 superheated steam and of alkalies. This is not true, however, for all mucins, for 

 several kinds yield gumlike substances which represent nitrogenous bodies de- 

 rived from the carbohydrates. 



3. Cellulose forms the chief constituent of the cell walls of all plants and 

 exhibits an organic structure. To obtain pure cellulose plant fibers are digested 

 successively with different reagents, such as dilute acids and alkalies, potassium 

 chlorate and nitric acid, alcohol and ether. The cellulose remains as the insolu- 

 ble residue. 



Table showing the percentage composition of the most important 



this chapter : 



^stances discussed in 



REFERENCES. The text-books of physiological chemistry: of Bunge, second 

 English edition by E. H. Starling, Philadelphia, 1902; of Halliburton, latest 

 edition, London and New York, 1904; of Hammarsten, fourth English edition 

 by John A. Mandel, New York, 1904; of Neumeister, second edition, Jena, 1897. 

 0. Cohnheim, " Chemie der Eiweisskorper," Braunschweig, 1900. F. Hofmeister 

 in "Ergebnisse der Physiologic," I, 1, Wiesbaden, 1902. A. Kossel, " Ber. d. 

 deutschen Ges.," 34, 3, 1902. 



