by the Method of Dark-ground I Humiliation. 627 
it has been shown that a slight change occurs on fixation, although the gel 
structure here very nearly approximates to that presented by the coagulated 
protoplast. Hence it seems probable that this gel condition is not like that 
of the partially irreversible coagulated sol, but is somehow a condition inter- 
mediate between the sol and the true gel — a condition which is in the main 
reversible. As a mere suggestion, it may be that the reversible portion only 
forms a gel network, enclosing the non-coagulated irreversible portion in its 
meshes, or holding it as an absorption compound, so that the whole mass is 
reversible. 
It seems probable that this state is also to be attributed to the proto- 
plasm of those cells which show none of the sol characters — it is really in 
this intermediate gel condition. In fact, as has been already mentioned, 
from various considerations there is reason to suppose that the gel is a really 
active vital state, capable of performing the functions of growth and 
nutrition. 
Even in the hydrosol condition, it has. been seen that very marked 
variations in the structure exist, both in the nature of the colloid and the 
organization of the protoplast. The colloid particles vary in size from 
microsomes just visible in transmitted light, to sub-microns which probably 
grade into amicrons. Also, although the complex is possibly always more 
or less emulsoid in character, yet some cells, as for example the Cucurbit a 
hairs, show a much more marked emulsoid character than such a type as 
E lode a. 
Taking all these different states of the protoplasm into account, it is 
clear that ‘das Protoplasma sehr polymorph ist ’ (Gaidukov, TO, p. 61). 
The plasma of the nucleus, and, in the green cell, of the chloroplast, 
seems to differ considerably in properties from the general cytoplasm in 
those cases so far examined. The nucleus seems to consist of a nearly clear 
fine structured gel, which is considerably altered in structure by the action 
of the usual coagulation or fixing agents. The gel of the nucleus must 
undoubtedly be regarded as an active state of the protoplasm. The chloro- 
plast also has generally the appearance of a slightly translucent gel with 
very little heterogeneous structure. Hence both nucleus and chloroplast 
are to be considered as fairly sharply differentiated from the ordinary 
plasma. It seems also quite probable that a definite surface membrane is 
organized at the boundary of these two colloid systems in each case. 
Whether this membrane is to be regarded as a mere boundary surface, with 
the properties of the colloid surface, or as a coagulation membrane produced 
on the inside of the cytoplasm complex in each case, can hardly be for the 
present determined. 
The effect of fixing agents on the colloid complexes requires much 
further study, when it seems possible that some definite basis may be found 
for the selection of an agent in any special case. From the effects produced 
U u 
