248 PROTOPLASM 



the casein in milk which coagulates. The fluid whey, an aqueous 

 solution of salts, sugars, etc., separates from the casein coagulum. 

 There are thus in milk three quite distinct systems, intimately 

 associated, viz., an emulsion of fat, a dispersion of fibrous units 

 capable of forming a coagulum, and a solution of salts, etc., 

 permeating the whole. So it is with protoplasm. 



Investigations on the structure of cellulose give the best 

 possible insight into modern interpretations of the mechanism 

 underlying the behavior of colloidal jellies, including protoplasm. 



Fig. 127. — Three-dimensional model of a glucose molecule (an amylene oxide 

 glucose unit): circles with black spots are carbon atoms; those with rings are 

 oxygen atoms; the others are hydrogen atoms. {After 0. L. Sponsler.) 



The Structure of Cellulose. — ^The cellulose molecule is now 

 thought to be a chain built of rings of anhydrous glucose, CeHioOs. 

 This latter group has long been known to be the basic unit of 

 cellulose and all higher carbohydrates, but the number and 

 arrangement of the rings in the larger cellulose molecules were 

 not known. Sponsler has suggested the arrangement in Fig. 127, 

 which is of glucose (an amylene oxide glucose unit). The 

 generally accepted configuration for the entire cellulose molecule 

 is that in Fig. 128, where each anhydrous glucose ring is joined 

 to its neighbor by an oxygen bridge, and every alternate ring 

 is the reflected image of the one on each side of it; i.e., it is 

 rotated through 180 degrees. Two such rings constitute an 

 anhydrous molecule of the sugar cellobiose, C12H22O11. Some 

 forty or more of these rings, so-called glucose "residues," joined 

 in a continuous chain, form the cellulose molecule. 



The linear cellulose molecule has at each end an apparently 

 unsatisfied valence bond. There is little likelihood that such 



