534 SUMMARY OF CURRENT RESEARCHES RELATING TO 



portion of the albumen is carefully drained off, leaving onlj' the 

 vitellus and the box with its coagulated contents in the shell. 



3. The shell may now be filled with absolute alcohol until the 

 yolk is completely covered, and then left for some hours, during 

 which the more superficial layers of the yolk harden sufficiently to 

 form a shell-like envelope of the softer central portion. 



4. The triangular mass formed by the box, and the hardened 

 albumen, is now ready to be cut out, in the same manner as in the 

 osmic acid method. During this process, the paper box may become 

 detached, either spontaneously, or with some assistance ; or it may 

 adhere so firmly that it cannot be safely removed. There is no 

 inconvenience in leaving it in place, as it will cut easily when the 

 piece is ultimately sectioned. 



5. The piece is further hardened twenty-four hours in absolute 

 alcohol, then preserved in alcohol of 36° (80 per cent.). 



III. Hot Chromic Acid. — 1. Treat with osmic acid as in I. 



2. Place the whole in a solution of chromic acid, and heat to the 

 point of boiling, over a water-bath. 



3. After cooling, cut out the triangular piece as in I. (6), leave it 

 for a few days in chromic acid, then transfer to alcohol. 



Imbedding and Cutting. — Duval imbeds, after each of the fore- 

 going methods, in collodion. The surface of each section is col- 

 lodion! zed some seconds before drawing the knife, by allowing a drop 

 or two of thin collodion to flow over it. 



Staining. — The sections are placed in serial order on a slide, and 

 then covered with picro-carmine, strongly diluted with glycerin. 

 The sections may be left in the staining fluid twenty-four to forty- 

 eight hours, the admixture of glycerin preventing drying. After 

 they are sufficiently coloured, the staining fluid is allowed to drain 

 ofi", and the slide is carefully washed with a pipette. The sections, 

 still in place, are treated with successive grades of alcohol, and then 

 mounted in balsam after being clarified in benzine (" benzine coUas "). 



Mounting the Blastoderm in toto.* — During the first three or 

 four days of incubation. Dr. C. O. Whitman has obtained good 

 surface preparations of the blastoderm in the following manner : — 



1. Break the shell by a sharp rap of the scissors at the broad 

 end; then carefully cut away the shell, beginning at the place of 

 fracture and working over the upper third or half. 



2. After removing as much of the white as possible without injury 

 to the blastoderm, place the rest of the egg, while still in the shell, 

 in a dish of nitric acid (10 per cent.), deep enough to cover it. 



3. The coagulated white should next be removed from the blasto- 

 derm by the aid of a brush or a feather, and the egg then allowed to 

 remain in the acid thirty minutes. 



4. Cut round the blastoderm with a sharp-pointed pair of scissors, 

 taking care to cut quickly and steadily. After carrying the incision 

 completely round, float the blastoderm into a watch-glass, keeping it 

 right side up and flat. 



* Whitman's 'Methods in Microscopical Anatomyand Embryologj',' 1885, pp. 166-7. 



