PROCEEDINGS OF SOCIETIES. 249 



seen on the starcli-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 tlie 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 wlieaf-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 ovid or globular, slightly atiherent 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- 

 stance during the process of digestion. The other structures seen 

 in the pea are carefully described ; the must curious among them 

 being the cells composing the external layer of the testa, which 

 bear so strong a resemblance to columnar epithelium of the intes- 

 tine, that they might be mistaken for the latter by an inattentive 

 observer. 



The sui)stances submitted to experiment were, — 1, boiled wheat- 

 starch ; 2, wheaten bread ; 3, uncooked tons les mois ; 4, boiled 

 tous les mois ; 5, boiled potato ; 6, uncooked peas ; 7, boiled peas; 

 8, boiled peas after ligature of the bile-duct; 9, boiled potatoes 

 after ligature of the bile and pancreaiic ducts. Several subsidiary 

 experiments were made to determine the action of the intestinal 

 mucus, the saliva, and the substance of the pancreas, on starch. 



The conclusions at which the author arrives from the experiments 

 are, — 



1. That the starch-granule is composed of two parts, chemically 

 and histologically distinct, — a cell-membrane and homogeneous 

 contents. The markings seen on many varieties of starch are re- 

 ferred to folds or markings of the in\ esting membrane. 



2. No perceptible change occurs in tlie starch, whether raw or 

 cooked, during its sojourn in the stomach of quadrupeds or the 

 ventriculus succenturiatus and gizzard of birds ; all the granules 

 preserve their perfect reaction with iodine ami their pristine ap- 

 pearance. 



