6o MORPHOLCGV OF THE CELL. 



envelopes. The internal organisation depends, in these cases, on a definite relation 

 of the water and the molecules of starch; the stratification of a starch-grain dis- 

 appears, like that of a cell-wall, when the water is removed from it [e. g. by evapo- 

 ration or action of absolute alcohol, &c.), because the more watery layers then 

 become similar to the less watery ones, and the difference of refractive power in 

 the two ceases. In the same manner the stratification also disappears when the 

 substance of the grain is rendered capable by chemical means (as dilute potash solu- 

 tion) of absorbing large quantities of water ; the denser layers absorb relatively more 

 water ; they thus become similar to the more watery layers, and it is no longer possible 

 to distinguish between them. 



Besides the differentiation in the proportion of water which is recognised in the 

 form of stratification, there is also in every grain an increase from without inwards 

 in the amount of water. This is partly ascertained by the refraction, partly by the 

 regular decrease of cohesion from without inwards. If the water is removed from 

 fresh starch-grains, fissures are formed which cross the layers at right angles; in the 

 interior a cavity is formed from which the fissures radiate ; these become narrower 

 outwardly, and are widest in the centre. From this it follows that on drying the 

 greatest loss of water occurs in the interior, and that this regularly decreases towards 

 the outside ; but it also follows that the cohesion of the layers is less in the tangential 

 direction (at right angles to the fissures) than in the radial. This points to the con- 

 clusion that within every layer the loss of water is greater in the tangential direction 

 than in the radial. 



If the water be removed from a fresh starch-grain or from one which has taken 

 up as much as it can, it contracts; the molecules contained in it approach one another 

 as their envelopes of water become thinner. A similar change takes place if the 

 granulose is removed from a grain ; the farinose-skeleton of the grain which remains 

 is, although saturated with water, much smaller than the original grain. This possibly 

 results from the fact that the molecules, now consisting only of farinose, possess less 

 attraction for water, and, having thinner envelopes, approach nearer; the cause may 

 however also be that the number of molecules has diminished. 



(b) The Extraction of the Granulose of starch-grains, leaving behind a skeleton of 

 farinose, can be brought about in very different ways: — i. By maceration in saliva at 

 an elevated temperature; in the starch of Canna indica the extraction, according to 

 H. von Mohl, is slow at 35°-40° C, but is accomplished in a few hours at 5o°-55° C. ; a 

 lower temperature suffices for wheat-starch, a higher is required for that of the potato ; 

 Nageli gives in general 40°-47° C. 2. According to Melsens a similar extraction may also 

 be effected by organic acids, diastase, and pepsin. 3. According to Nageli it can be 

 accomplished also by very slow action of hydrochloric or sulphuric acid which has been 

 so diluted with water that it does not cause the starch-grains to swell. 4. According to 

 Franz Schulze, the granulose is extracted in from two to four days by a saturated 

 solution of sodium chloride containing i p. c. of hydrochloric acid, at a temperature of 

 60° C; the residuum, which perfectly exhibits the organisation of the starch-grain, 

 amounted, according to Dragendorfl", to 57 p. c. in potato-starch, 2*3 p. c. in wheat- 

 starch. These skeletons are not coloured by iodine (Nageli's preparation with sul- 

 phuric acid after fifteen months' extraction), or they become copper-red, and in 

 places where the extraction was not perfect, bluish. They do not swell in boiling 

 water, i. e. do not form paste. At 70° C. the whole of the starch-grain, according to 

 Mohl, is dissolved in saliva; the skeleton produced at 40°-55° G. is, however, not affected 

 by saliva at 70°. 



Within the living cell the starch may be dissolved in very different ways ; probably 

 solution occurs mostly under the influence of protoplasm, or by the assistance of 

 nitrogenous combinations in the cell-sap. Sometimes the solution begins, as in the 

 extractions mentioned above, with the removal of the granulose, the farinose remaining 

 behind; but this often takes place only partially; the extraction proceeds in places 



