Royal Society. 461 



were still seen when the granules were viewed by polarized lio-ht, 

 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-ceils, 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 

 compression of the starch-granules within an inelastic cell-mem- 

 brane. 



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 most 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 substances submitted to experiment were, — 1, boiled wheat- 

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

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

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

 after ligature of the bile and pancreatic 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 investing membrane. 



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

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

 ventriculus sucoentuiiatus and gizzard of birds ; all the granules 

 preserve their perfect reaction with iodine and their pristine ap- 

 pearance. 



3. The conversion of boiled starch into dextrine and glucose is 

 chiefly effected in the first few inches of the small intestine, but it 

 continues to take place in a less degree throughout the entire intes- 

 tinal canal. 



4. In the digestion of boiled wheat or other starch, or of wheaten 

 bread, the bulk of the mass rapidly diminishes in its passage through 



