33 



the starch granule is absolutely dry, these solid particles— to 

 which Nageli gave at first the name of molecules— apparently 

 come into perfect contact, for the granule does not lose its 

 transparency, which would be the case if air were included in 

 its substance. Hence the first inference we may draw from 

 this as to the form of the molecules, is that the particles are 

 not spherical or oval, for in that case the starch grains would 

 of necessity contain air when dry. They must be, therefore, 

 more or less polyhedral, but they are not equi-axial, since the 

 swelling up does not take place equally in all directions. The 

 word molecule used at first by Nageli to designate these solid 

 particles has not the same sense as when it is used in Chemistry, 

 for one of these molecules of Nageli is probably an aggregation 

 of a larger or smaller number of chemical molecules ; and, 

 therefore, in order to avoid any confusion on this score, the 

 word micella has been substituted by him in his more recent 

 works. These micellae may be supposed to be of various sizes, 

 and it is evident that, if the thickness of the aqueous envelope 

 be the same, larger micellae will form a more dense, and smaller 

 micellae a less dense structure. It is well known that organized 

 structures, such as the cell-wall and starch grains, exhibit an 

 appearance of stratification when examined under the micro- 

 scope — that is to say, of an alternation, in one or more planes, 

 of more and less dense layers ; — these were formerly supposed 

 to indicate the successive layers of deposition of cellulose in the 

 one case and of starch in the other — internally in the case of 

 the cell-wall, externally in the case of the starch grain ; while 

 in reality the appearance is due to an alternation of layers 

 containing larger and smaller micellae. In all cases the pro- 

 portion of solid to fluid is greater in the dense than in the less 

 dense layers; or, in other words, the relative size of the 

 micellae to the watery areas which surround them is greater in 

 the layers of greater density. 



The changes in volume of organized bodies due to the 

 removal of water or its absorption, depend, then, on the fact 

 that when swelling up takes place the micellae are forced farther 

 apart by the water which penetrates between them, while, on 



