624 Price . — Some Studies on the Structure of the Plant Cell 
quickly. The only method which was used to any extent was to take the 
reagents in a more concentrated form than is required for fixation, and to 
draw them under the edge of the cover-glass by means of a small piece of 
filter-paper placed at the opposite edge. The reagent is thus considerably 
diluted, and in most cases only watery solutions could be used. Also it is 
almost impossible to know at what instant the fixative reaches the object in 
question, practically the only test being the observation^ of the first reaction 
on the cell-contents. Thus, no comparisons of the rates of coagulation by 
the same reagent in different concentration were obtained, nor of accurate 
comparisons of the rates of fixation by different reagents. It is hoped that 
this may, however, be possible at some future time. The actions described 
are merely general statements of the actions of the reagents and the 
resulting structures of the protoplasts. 
The material used has been very largely Spirogyra and Elodea ; both 
are obtained easily, and both have proved very good objects for dark- 
ground work in most directions. 
The general reaction which occurs on fixation is of course a coagulation 
of the hydrosol, but as the gel appearances produced by different fixatives 
differ quite markedly, it must be concluded that the process is something 
more than a mere coagulation (Fischer, ’ 99 , pp. 1-7 1). The change is 
indicated in dark-ground illumination by a complete alteration in structure ; 
the hydrogel produced has generally the appearance of a large number of 
overlapping diffraction images, rather bright and milky and with no move- 
ment of the particles. Like the various sol states, the gels differ considerably 
in character and general appearance. 
A short description of the action of some fixatives on various types of 
material will now be given. 
Osmic Acid. A 1 per cent, solution was run under the edge of the cover- 
slip, Spirogyra was chiefly studied. In this case the first action is to 
produce an extremely fine precipitate in the cell-sap, which under the lower 
powers was first mistaken for the milkiness of fixation. This precipitate 
is very probably produced by the presence of tannins in the cell-sap 
(Tunmann, T 3 , p. 255), and with this type of illumination very much 
resembles the precipitate which caffeine and antipyrin give with tannins 
in the same way (ibid., p. 258 ; Wisselingh, van, TO). The precipitate 
gradually aggregates into larger particles which eventually become motion- 
less. The protoplasm assumes a coarsely granular milky appearance, but 
where observation is good (where the precipitate is less) the microsomes 
of the protoplast can be seen, apparently fixed as such, and lying in the 
coagulated substratum (PI. XLI, Fig. 5). Thus really comparatively little 
change occurs except the cessation of the motion of the colloid particles and 
the formation of a gel network. 
In a cell plasmolysed with 30 per cent, cane sugar, and fixed with 
