CONDITION OF AGGREGATION OF ORGANISED STRUCTURES. 669 
a violent swelling takes place in cellulose and starch-grains, and they pass into a pasty 
state. Protoplasmic substances, on the contrary, coagulate, as they do under the in- 
fluence of higher temperatures. Concentrated sulphuric acid finally completely destroys 
the micellar structure of both with a smaller or larger amount of chemical change, and 
they deliquesce. 
(c) Solution of Potash acts on starch-grains like sulphuric acid, especially in causing 
them to swell up. Its action on protoplasmic substances is on the other hand very 
different from that of acids ; if the solution is dilute they swell up strongly or deliquesce, 
and this is especially the case with protoplasm and the nucleus of very young cells (the 
nuclei of older cells often resist the action strongly). But in a highly concentrated 
solution of potash protoplasmic structures often retain their form and apparently their 
structure; they neither coagulate nor deliquesce. The fundamental destruction of their 
micellar structure which has nevertheless taken place is evident from the fact that they 
immediately deliquesce if water is added copiously. 
{d) Mechanical Influences. Organised structures bear without injury mechanical forces 
such as pressure, impact, or slight traction ; they are either sufficiently elastic, like starch- 
grains and cell-walls, again to bring into equilibrium the changes which are thus caused 
in their internal tension and external form ; or they are inelastic like protoplasm and 
chlorophyll-granules, and can then equalise small passive changes of form in another way. 
But stronger forces cause disruptions of the micellae which cannot be again effaced. 
The micellar structure of the separated portions may however still be perfectly retained, 
as is shown by fragments of starch-grains and cell-walls. This is still more evident 
in motile protoplasm, where the separated portions of the previously continuous sub- 
stance behave like so many individuals, and have the power of independent motion ; 
as, for example, separated portions of plasmodia, the detached halves of the rotating 
protoplasm in the root-hairs of Eydrocharis when contracted by a solution of sugar, &c. 
In the same manner tv^'O or more separated portions of protoplasm may unite into a 
whole, as in the formation of large plasmodia and of zygospores, the fertilisation of 
oogonia, &c. The only purely mechanical mode in which complete destruction of an 
organic structure can be accomplished is by crushing; i.e. by complete disseverance 
of its micellae and their subsequent promiscuous intermixture. In this case a chemical 
change usually directly follows the mechanical destruction of the micellar structure of 
the protoplasmic substance. In some cell-walls the mere interruption of continuity by 
a cut causes striking changes in the adjoining and the more distant parts ; thus, accord- 
ing to Nägeli, cell-walls of Schixomeris that have been cut through become shorter and 
thicker to a remarkable extent. 
[e) Changes in the micellar structure of organised structures caused by injurious 
influences determining their death are often accompanied by striking changes in their 
relations to diffusion. With respect to stafch and cellulose but little is known in this 
respect ; but the phenomena connected with protoplasm, including the nucleus, are very 
remarkable ^ Normal living protoplasm does not, for example, absorb any colouring 
material from the surrounding solution ; but as soon as it has been killed by heat or by 
a chemical reagent, the dissolved colouring material not merely penetrates into it, but 
accumulates in it to such an extent that the dead protoplasm appears of a much deeper 
colour than the surrounding solution of the colouring substance. Starch and cellulose, 
on the contrary, even in a fresh unchanged condition, absorb from a solution of iodine 
a comparatively much larger quantity of iodine than of the solvent, and become of a 
much deeper colour than the surrounding solution ; the colour is also different, usually 
blue, while the surrounding solution is yellowish brown. The protoplasm which fills the 
cells and has been killed in any manner, by frost, heat, or chemical agents, is more 
^ Nägeli, Pflanzenphysiologische Untersuchungen, vol. I. p. 3 et seq. — Hugo de Vries, Sur la 
permeabilite du protoplasm des betteraves, Arch. Neerland. vol. VI, 1871 : [also id., Unters, ueb. 
die Mechanischen Ursachen der Zellstreckung, 1877. — Pfeffer, Osmotische Untersuchungen.] 
