114 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



different " meals," by the shape and size of the granules, will thus permit 

 of the recognition of adulteration with inferior meals : — 



Mm. 



Starch-granules from Potatoes (average), 0.140 (0.10-0.185). 



" Arrowroot, " 0.140 



" Sago, •' 0.07 



•■ Beans, " 0.063 



■' Peas, " . 0.050 



" Wheat, " • 0.050 



" Eye, " 0.036 



" Oats, " • 0.031 



•■ Corn, " • 0.02-0.03 



" Tapioca, " . 0.028 



" Rice, " 0.022 



" Barley, " 0.025 



" Buckwheat, " 0.009 



The striated appearance is due to the fact that starch is composed 

 of two substances, — cellulose and granulose, arranged in concentric 

 layers, the cellulose always being external. Granulose stains blue with 

 iodine, — not by the formation of a chemical compound, but by the deposit 

 of the iodine around the starch-molecules, — and cellulose stains a faint 

 yellow. These two substances may be separated'by digesting, at 60° C, 

 one part of starch in forty parts of saturated salt solution containing 

 1 per cent, of free hydrochloric acid. The granulose then passes into 

 solution, while the cellulose remains. Examined in this way, potato- 

 starch has been found to contain 5.7 per cent, cellulose, wheat-starch 

 2.3 per cent., and arrowroot 3.10 per cent. Under the action of dias- 

 tatic ferments granulose is converted into sugar, while cellulose remains 

 unaltered. A third substance has been distinguished in starch which is 

 termed erythrogranulose, and it differs from granulose in taking on a red 

 coloration when treated with iodine. It has a stronger affinity for iodine 

 than granulose. Hence, when starch-mucilage is treated with very dilute 

 iodine solution a red color is produced, but when a large quantity of 

 iodine is added, a deep-blue coloration, from the fact that the reaction 

 of the iodine with the granulose masks the erythrogranulose reaction. 



Pure starch is a white, tasteless, and odorless substance which is 

 almost entirely insoluble in cold water. In boiling water the granules 

 swell up from the imbibition of water by the granulose, the cellulose 

 envelopes burst, and the granulose dissolves. It is to the presence of 

 the cellulose envelope that the insolubility of raw starch in cold water is 

 due. When the cellulose membranes are destroyed or comminuted, as by 

 grinding with powdered glass, a part of the granulose is then dissolved 

 in the water, and by repeated washing nearly all the granulose may he 

 removed and the cellulose envelopes alone remain. In boiling water, 

 while the starch is said to be soluble, the condition is more strictly one 

 of a high degree of imbibition of the starch. Like other colloids, starch 

 is incapable of dialysis, and forms a mucilaginous emulsion. A solution 



