by the Method of Dark-ground Illumination . 623 
wall. In no case with this method have intercellular connexions been made 
out, however, although numerous attempts have been made to observe them. 
As described by others, the threads pass to the side as well as the 
end walls, and can be produced in coeonocytic material such as Vaucheria . 
In this case the threads always seem to be stretched, and to show no motion 
whatever. 
It is somewhat difficult to relate these fibrils in structure to the general 
colloid complex of the protoplasm. If a boundary layer of gel is produced 
by the action of the plasm olysing agent, or the salts in the escaping cell-sap, 
these fibrils should be thus bounded, and apparently should consist entirely 
of a thread of hydrogel, on account of their small size. They may certainly 
have this nature, and may be regarded as fine strings pulled out from the 
outer layer of the protoplast, like fine strings from a coagulating jelly. 
The activity of the particles, both at the walls and at the junction of the 
thread with the contracted protoplast, is, however, hardly accounted for on 
this hypothesis, unless we regard the gel layer to be so thin as to be formed 
only at the outside of these little processes, and to be quite invisible. 
After fixation of the protoplast, the threads usually continue their 
oscillating motion. This rather indicates that this is to be regarded as 
Brownian movement set up by the molecules and microns in the liquid 
which surrounds the fibrils. 
It seems impossible as yet to decide whether these fibrils are really 
functionally concerned in the process of plasmolysis, or whether they are to 
be regarded as artifacts due to the contraction of a viscous coagulable fluid. 
§ 9. The Action of Fixing and other Reagents on the 
Plant Cell. 
Since it is possible by this method to determine very clearly the point 
of coagulation of the protoplasmic hydrosol, it seemed that it would be of 
interest to compare by this the relative and absolute effects of various fixing 
agents and other reagents on the plant cell. Such a study might do some- 
thing to decide as to the relative merits of fixing and killing agents, and to 
the possible extent and nature of the artifacts, which are presumably 
produced to a greater or less extent by all these agents. In such an 
observation the time factor as well as the resulting structure must be taken 
into account ; and in this direction was encountered an experimental 
difficulty which has not as yet been completely overcome. In spite of this, 
the rough results show some features of interest and seem quite worth 
recording although necessarily incomplete. The difficulty is that of allowing 
the fixing fluid to flow quickly on the object, while the latter is under 
observation on the stage of the microscope, and in optical continuity with 
the sub-stage illuminator. The fresh objects have to be mounted in water 
and adjustments made, and then some means is required of irrigating them 
