SWELLING OF ORGANISED BODIES. 207 



Crystals are either solul)le in water or not. In the latter case the water which 

 is in contact with the crystal, in spite of the force of attraction which exists between 

 both, is unable to tear off any molecules; and the construction of the insoluble 

 crystal also prevents the entrance of water molecules into its interior. If the crystal 

 is soluble in water, however (as a cube of common salt for instance), the attraction 

 between the two substances results in molecules being torn off from the surfaces 

 of the crystal, and intercalated between the molecules of the water. 



By this means molecules of the salt l\ing deeper come into contact willi 

 the water, and suffer the same fate in it, until the whole crystal is dissolved into 

 its molecules, which now move about within the mass of water; and this movement 

 continues until a completely uniform distribution of the salt molecules in the mass 

 of water results. With the attainment of this condition of equilibrium, where every 

 salt molecule is surrounded by exactly as many molecules of water as ever}- other 

 in the same solution, relative rest now occurs. If, instead of the common salt, a 

 small portion of Iodine had been placed at the bottom of a large vessel filled with 

 Avater, a watery solution of Iodine would have l^een formed in the same way; 

 and the uniform distribution of the Iodine molecules in the water would be 

 recognisable at once in its uniform colouradon. This condition of equilibrium, 

 however, we could at once bring into a condition of movement if we suspended 

 in the upper part of the solution a bag filled with starch. The Iodine molecules 

 coming immediately in contact with the starch, would then penetrate into the 

 starch grains, affording opportunity to the more distant Iodine molecules also to 

 move towards the starch ; and this process would continue until all the Jodine 

 molecules, even the most distant ones, had travelled from the bottom of the vessel 

 up to the bag of starch, and therefore in opposition to gravitation. 



Organised bodies — to which, so far as the plant is concerned, we may consider 

 the cell-wall, the protoplasm and nucleus, starch-grains, and the so-called crystalloids 

 to belong — behave towards water quite differently from insoluble and soluble crystals. 

 If a dry body of this kind is laid in water, its volume is increased more or less 

 according to circumstances, and by this the consistence of the body is altered. 

 Previously hard and brittle, it now becomes soft and flexible. A closer examination 

 at once shows that the increase in volume which the body has undergone by 

 swelHng up in water, is almost equal to the volume of the water which it has 

 absorbed. If this so-called imbibed water is again withdrawn from the swollen bod}-, 

 by evaporation or by means of some medium which abstracts water, c. g. absolute 

 alcohol, its volume again shrinks until it has reached the original size. Between 

 the organised body capable of swelling and the water, there exists a mutual at- 

 tracdon, just as between water and a soluble crystal. The great difference between 

 the two, however, lies in that the molecules of the latter become separated from 

 one another and distributed between the molecules of the w-ater; in the swelling 

 of an organised body, on the other hand, the water penetrates between its micellse 

 without these completely losing their connecdon. They only separate further from 



suggested that protoplasm also is an organised sut)stance in Nsegeli's sense : it had previously been 

 regarded as a structureless slime or even as a lluid. This view established by me, that protoplasm 



is an organised body, is now generally accc[4ed. 



