ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
153 
dispensed with. It was found most satisfactory to remove the ovum 
from the action of the reagent as soon as the translucent protoplasmic 
germ-disc turns whitish opaque, which takes place very quickly, and 
to complete the separation of the blastoderm in dilute glycerin. The 
separated blastoderm may afterwards be stained with dilute Schneider’s 
acetic carmine, or with Ehrlich’s hematoxylin, and theu mounted in 
glycerin ; or it may be left unstained, for most things can be satisfac- 
torily made out without any staining, and by avoiding this unnecessary 
process of technique the risk of injuring or dislocating the blastoderm is 
greatly lessened. Treatment of living eggs with Perenyi’s fluid for a 
few seconds is excellent for the surface study of cleavage ; it turns the 
protoplasmic portion of the ovum opaque yellow, and brings out the 
cleavage furrows distinctly, while the rest of the egg remains translucent 
as before. 
Mode of Investigating Bryozoa.* — Mr. C. B. Davenport found that 
the Gymnoloemata present many difficulties to finer technique ; their 
chitinous covering is often very thick, and there is frequently, in 
addition, a calcareous skeleton. When the latter is present, picro-nitric 
acid mixed with sea-water is a fairly good fixing reagent ; when it is 
absent, hot corrosive sublimate is the most serviceable. Extreme 
caution must be taken in transferring the objects through the grades of 
alcohol, so as to avoid the collapse of the ectocyst ; the author made 
use of the chloroform-paraffin method of imbedding in order to make 
the transfers more gradual. The best staining agents were alcoholic 
dyes like Kleinenberg’s hfematoxylin and Mayer’s cochineal, though 
Ehrlich’s hseiuatoxylin was often used with success. 
Method for demonstrating Structure of Spinal Cord and Cere- 
bellum. | — Prof. A. Van Gehuchten, from a series of observations made 
on the spinal cord and cerebellum, confirms the original statements of 
Ramon y Cajal, who in his researches followed the technique devised by 
Golgi with some slight modifications. 
The spinal cord and cerebellum, in the embryonic, newly born, and 
adult conditions, of several kinds of mammals and also of the fowl, were 
used for the purposes of these observations. 
The author’s practice was to place small pieces of nervous tissue in 
a mixture of 3 per cent, bichromate of potash and of 1 per cent, osmic 
acid in the proportion of 4 parts bichromate to 1 part osmic acid. The 
pieces, several millimetres thick, usually remained in the mixture for 
two to two and a half days at the ordinary temperature, but fixation 
can be hastened by keeping them at a temperature of 35° to 40° for 
thirty to forty hours. On removal the pieces are rapidly washed in 
distilled water, and then immersed in the 3/4 per cent, nitrate of silver 
solution, whereby a precipitate of chromato of silver is deposited in the 
nervous tissue. The addition of one drop of formic acid to 100 ccm. of the 
silver nitrate solution considerably aids reduction, the precipitation 
commencing immediately on immersion of the pieces in the bath, wherein 
they remain for at least twenty-four hours, but a still longer stay is not 
harmful, provided light be carefully excluded. 
* Bull. Mus. Comp. Zool., xxii. (1891) p. 3. 
t La Cellule, vii. (1S91) pp. 81-122 (4 pis., 55 figs.). 
