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normal digestion, and after cutting off the supply of bile and pan- 

 creatic juice. 



The correct appreciation of the structure of the starch- granule is 

 of considerable importance in relation to these investigations, and 

 the author believes that he has been able to afford a satisfactory 

 solution of this vexed question. The changes observed during the 

 digestion of starch favour the original opinion of Leuwenhoeck, that 

 the starch-granule consists essentially of an investing membrane or 

 cell-wall, enclosing an amorphous matter, the true starch, which 

 strikes an intense blue colour with iodine ; and these changes also 

 support the opinion of Professor Quekett, that the concentric circles 

 seen on the starch-granules of many plants are simple foldings of 

 the investing membrane, leaving it still doubtful, however, whether 

 these concentric circles are not in the starches of some plants com- 

 posed of linear series of dotted elevations or depressions of the in- 

 vesting membrane. 



By these experiments it was determined that the concentric circles 

 remain after the whole of the starch matter, colourable by iodine, 

 was removed, and that even then the characteristic cross and colours 

 were still seen when the granules were viewed by polarized light, 

 although more feebly than before ; this result being probably due 

 to the lessened power of refracting light, after the removal of the 

 starch matter. 



After describing the structure of the wheat-grain and flour, the 

 changes occurring in the wheat-starch during the manufacture of 

 bread are given in detail ; but the most interesting of the changes 

 produced by cooking are those seen in the boiled or roasted potato 

 and in the boiled pea. 



In each of these the act of cooking effects two purposes : it 

 causes great enlargement and physical change of the starch-granules, 

 and dissolves the intimate adhesion of the starch- cells, which after- 

 wards appear as ovoid or globular, slightly adherent bodies distended 

 by the swollen starch- granules, the outlines of which are indicated 

 by more or less irregular gyrate lines, produced by the mutual com- 

 pression of the starch-granules within an inelastic cell-membrane. 



The starch-granules of the pea possess a much thicker investing 

 membrane than those of the potato, which causes their outlines to 

 remain much more distinct after the removal of the true starch sub- 



2 A2 



