456 PROTOPLASM 



transformed in the living world, the simple sugars are the key 

 substances concerned. Respiration is, however, not the only- 

 physiological process in which the sugars play a prominent part. 

 Muscular action involves glucolysis, or the conversion of glycogen 

 (starch) into glucose; and glycogenosis, the return from glucose 

 (or lactic acid) to glycogen. The body utilization of the lower 

 carbohydrates is an important problem in the study of cancer. 

 The total blood sugar is high in cancer and in diabetes, but the 

 utilization of this sugar (oxidation to lactic acid) is rapid in 

 cancer, with attendant rapid cell growth, while it is sluggish in 

 diabetes. 



Starches. — The higher carbohydrates — the polysaccharides or 

 nonsugars — are mostly insoluble in water, but they take up 

 water readily and form pastes and jellies; they are therefore 

 colloidal. 



The starches are sometimes referred to as amyloses and, together 

 with the celluloses, as hexosans, because on hydrolysis they 

 yield hexose sugars: 



(C6Hio05)x + (H2O). = a-CeHisOe 



Starch is one of the most widely distributed of substances in the 

 vegetable kingdom ; it is the chief storage food of plants and may 

 constitute 70 per cent of the dry weight of seed. The structure 

 of the starch grain, as it occurs in the plant, is very characteristic 

 and is used as a means of identification. Its chief distinguishing 

 feature is its layered or lamellar structure (Fig. 11). Starch 

 is of biological importance because of its nutritive qualities, its 

 extraordinarily high imbibition pressure, and its paste-forming 

 qualities. Whether or not the imbibition pressure of starch is 

 in part responsible, as has been maintained, for the carrying of 

 water to the tops of trees cannot be said, but it certainly plays a 

 part in bringing water into the cell. The gelatinous properties 

 of starch may, to a great extent, be responsible for the highly 

 viscous properties of protoplasm. Starch paste has some of the 

 properties of a true elastic jelly and some of those of a plastic 

 mass (page 227), but much of the viscous, glutinous, and elastic 

 properties that one might be inclined to attribute to starch, e.g., 

 in such substances as bread dough, are in great measure due to 

 associated matter. Gluten comprises 10 per cent of wheat. 



