by the Method of Dark-ground I Humiliation. 625 
osmic acid, the larger microsomes also remained as ‘ nodes ’ in the gel. 
The bases of the fibrils also were fixed, and still give the appearance of 
being continuous with the outer skin of the protoplast. The broken fibrils 
retain their oscillating movements, indicating that this movement is a direct 
Brownian effect on them per se. 
In the case of Cucurbita hairs the penetration and fixation were 
very slow. 
Acetic Acid. Glacial acetic acid run under the cover- slip furnishes 
a rapid coagulating agent, which, however, in the conditions used, often 
causes considerable alteration of form and contractions of the protoplast. 
The hydrogel produced is rather opaque, and shows no microsome structure 
but a collection of overlapping diffraction images. 
In Elodea the first action was observed to take place on the nucleus. 
Almost instantly this begins to become highly dispersive, the light being 
nearly all scattered by the surface layer. It soon shows a coarse gel structure 
as in PL XLI, Fig. 9. On the cytoplasm the action is not nearly so 
marked, but a rather finer structured opalescent gel is produced. 
On Spirogyra , the hydrogel produced is rather milky, and of a fine 
structure, but fixation is apparently fairly good. The walls of the vesicles 
of cells, plasmolysed to show them, usually altered in shape, as though they 
were elastic and subjected to sudden changes in pressure. The wall was 
fixed as a rule without any escape of the contents of the vesicle, and was 
converted into a membrane composed of a fine structured gel, which is 
practically opaque to oblique light. 
In the hyphae of Mucor the effect was almost instantaneous, the proto- 
plasm, sol and gel alike, being converted into an opaque gel composed 
of overlapping diffraction images of the nodes. 
Mercuric Chloride. This was used in 0-5 per cent, solution, which of 
course became diluted before its action. In Spirogyra the effect was first 
observed on the nucleus and its surrounding cytoplasm. The cytoplasm 
coagulates and rounds off slightly ; the suspending threads themselves are 
fixed and still show the larger microsomes after fixation. The nucleus 
becomes more dispersive, and the nucleolar membrane more distinct. 
Chrom-acetic Fixing Agent. The fixation with this solution seems to 
produce much the same type of gel as that formed by acetic acid, differing 
from the microsome-fixation type described for osmic acid. 
Absolute Alcohol. This reagent used as described, that is, diluted with 
water before reaching the object, produces considerable deformation of the 
protoplast, breaking of the suspending threads of the nucleus, and so on, 
and a comparatively slow coagulation of the hydrosol to a milky gel. Thus 
used it is undoubtedly a bad type of fixing agent. 
