of Cellulose in Starch-grains, 243 



the saliva daily from the starch- grains, and wash them well, and 

 mix them with fresh saliva, since the putrefactive decomposition 

 of the latter would otherwise ensue, which produces destruction 

 of the starch-grains. 



The alterations undergone by the starch-grains are described 

 so accurately by Nageli that a repetition of the account is en- 

 tirely superfluous; I confine myself, therefore, to citing the 

 most general features, and to the discussion of those points 

 which appear to me of especial importance for the explanation 

 of the composition of the starch-grain. 



The first glance at the starch-grain robbed of its soluble con- 

 stituent by saliva shows that it has lost considerably in sub- 

 stance, since it possesses far less refractive power ; and its much 

 greater mobility in water, and the longer time it takes to settle 

 when stirred up therein, show that it has lost considerably in 

 weight. I could not determine how great this loss of weight is, 

 since this would require a different solvent, which could be 

 removed from the starch-grains entirely by washing, while in 

 the use of saliva many epithelial cells of the lining membrane 

 of the mouth remain mixed up with the granules. The estimate 

 of Nageli (p. 183), that in potato-starch the mass diminishes 

 from 7 or 8 to 1, may be correct, but it rests upon too insecure 

 a base to be depended upon with certainty. 



The magnitude of the grains diminishes far less than the 

 substance ; but the amount of decrease is very difficult to state 

 with certainty, on account of the very variable absolute size of 

 the individual grains ; and a great number of measurements 

 would be requisite to obtain an approximation to an accurate 

 determination. That a diminution of size does take place, may be 

 very distinctly seen in the starch-grains of germinating wheat, 

 in which the extraction of the soluble substance frequently pro- 

 ceeds, not uniformly from the margin to the centre of the dis- 

 coid grains, but in separate lines running in the direction of 

 radii, under which circumstance each of these streaks corre- 

 sponds to a notch or depression at the margin of the grain, 

 which indicates a collapse of the substance towards the interior. 

 Not only, however, is there a contraction of the substance in the 

 radial direction, but there is a still stronger contraction in the 

 direction of the separate laminae. This is shown very clearly by 

 the behaviour of those grains of Canna in which the solution 

 has affected only the outermost layers, when these latter laminae 

 frequently crack into polyhedral fragments, like dried clay, be- 

 cause the inner and still unaltered laminae oppose an insur- 

 mountable obstacle to their efforts to contract. A still stronger 

 contraction occurs in the laminae situated between the periphery 

 and the organic centre (likewise in the direction of the laminae), 



IG* 



