2 RAINEY, ON STARCH GRANULES. 



It may at first appear startling that substances so dissimilar 

 as carbonate of lime, as found in shells, or a mixture of car- 

 bonate and phosphate of lime, as it occurs in bone or dentine, 

 should have anything in common either in their structure or 

 in the manner in which they are formed ; but I may remark 

 that none of these structures is so simple, and so exclusively 

 mineral or organic as is generally supposed. The carbonates 

 and phosphates of a rounded form are all compounds of a 

 viscid substance and eaithy matter; and starch granules 

 have diffused through their structure a small quantity of 

 earthy matter. I have always found that starch burnt to ash 

 on platinum leaves a residue of lime ; but desirous to have 

 more precise knowledge upon this point, I availed myself of 

 the advantage of the assistance of Dr. Moldenhauer, the 

 chemical assistant at St. Thomas's Hospital, in making for 

 me a quantitative analysis of some potato-starch prepared 

 for the purpose. The result of which is, in 100 grains of 

 dry potato-starch — 



Dry starch . . . 8080 

 Water . . .18-94 



Ashes ... -26 



100-00 



These ashes Ave found to contain silica and phosphate of 

 lime ; the proportions I did not think it necessary to have 

 determined. However, the globular form of the carbonate 

 of lime, occurring in the deep layer of the shells of Crusta- 

 ceans, is as high in the physiological scale as the granules of 

 starch. 



In treating this subject I shall first consider the different 

 forms in which the particles of starch occur, and their re- 

 semblance to corresponding forms of certain solid bodies, 

 undoubtedly produced by the coalescence of their particles ; 

 and then I shall show that the chemical and mechanical 

 conditions necessary to produce such forms of starch exisl in 

 the vegetable organization. The various forms of starch 

 must be examined both when the starch is in the stareh- 

 cells and after it has been removed from them. Sections of 

 growing vegetables in which starch is formed in large quan- 

 tities, as in the very young tubers of potatoes, will serve for 

 this purpose. In such sections, in this and the majority of 

 plants, the starch-cells in the vicinity of the ramifications of 

 the vessels will be seen to contain very small spherules of 

 starch, many of them too minute to be accurately measured; 

 yet, notwithstanding their minuteness, their figure is well 

 defined, and they are made black or blue by iodine, proving 



