THE ORGANIC ELEMENTS. 13 



minute portion, immediately in contact with it, assumes a yellowish colour, 

 we may easily trace, under the microscope, every possible stage of transi- 

 tion in the gradual change ; which is very remarkable, and affords the 

 best explanation of the structure of the starch granule. The first action 

 here is naturally one of drying, by which the so-called nucleus is con- 

 verted into an air-bubble, appearing so characteristic that we can thereby 

 distinguish the use of dry heat, as, for instance, in the Mandiocca fa- 

 rinha. in Sago, &c. The individual layers simultaneously separate, and, 

 in consequence of drying out, the lines of separation become sharper, 

 blacker, broader, and even recognisable broader or narrower layers of 

 air ; the layers hang closer together at some places than at others, and 

 larger or smaller spaces are formed. By degrees the separate layers peel 

 away from each other, like the scales of a bulb, whilst an actual fusion 

 (conversion into gum) takes place at individual points. 



If we continue the action of water, heated gradually to the boiling 

 point, a change at first takes place, which is very similar to what has 

 been just described with reference to sulphuric acid. It is only in the 

 latter stages that the phenomenon is so far different, that the cleft in the 

 interior is gradually converted into a large cavity, when the whole 

 swollen granule looks like a compressed thick-skinned bag. 



By degrees the outlines grow more indistinct ; but the paste-like 

 mass, consisting of a granule, continues clinging together; and, on 

 looking under the microscope at the thinly boiled paste mixed with 

 water, we may, by means of iodine, recognise the separate and inflated 

 granules, whilst the water added is never coloured blue. I have not 

 been able to continue the boiling during several days, but I think I may 

 venture to conclude, from my own experiments, that starch may take up 

 a large quantity of water, and thus swell to a large volume (although 

 even this seems to have its limitations), but that it never can be properly 

 dissolved either in cold or boiling water. 



I will here finally mention the treatment of starch with cold water. 

 If starch be rubbed up, for the period of half an hour, in a mortar, with 

 double the volume of water, we obtain a viscid, almost stiff, salve, capable 

 of being drawn into threads. A large number of the granules then 

 appear under the microscope, to be crushed in various ways, torn and 

 broken up, partly ground into small flakes. The inner aqueous layers 

 are pressed and combined with more water by friction, as it appears, ex- 

 hibiting a finely floccular or granular, but connected, mass, which is 

 coloured blue by iodine, whilst all the actual fluid round (the water) 

 remains wholly uncoloured. 



All these experiments were frequently repeated with different impure 

 specimens of starch, such as are commonly bought, but all of the same 

 kind ; and the results were, in every case, essentially the same. Iodine 

 was always used in these experiments, and there never was the most 

 remote indication of there being any part in the starch granule which 

 was not equally coloured by it. There never occurred the slightest ap- 

 pearance, in these experiments, to refute the easily tested fact, that the 

 layers of starch granules are more aqueous in proportion as they lie fur- 

 ther to the interior : nor was the unimportant point refuted, that there 

 were slight differences in the external layers, arising from the adhesion 

 or infiltration of some few traces of albumen, fat, or wax ; these differ- 

 ences merely resulting in a longer or shorter delay of the action of the 

 solvents. The same experiments were constantly repeated with purified 

 starch, in order fully to test the correctness of the last-named facts. 



