30 ALLEN 



II. TECHNIQUE. 



I. Injecting Masses. 



Nearly every injecting mass and color has been tried, but the 

 most satisfactory, as well as the cheapest, proved to be a gelatin 

 mass, colored with Berlin blue or carmine, and Hoyer's lead 

 chromate yellow gelatin mass ; or, for tracing out fine vessels 

 and histological work, a saturated aqueous solution of Berlin 

 blue may be used. 



Berlin blue can be purchased in the form of a dried precipi- 

 tate and this dissolved in water, but a more satisfactory solution 

 is obtained by following the directions of Mayer (54, p. 310). 

 A solution of 10 c.c. of tincture of perchloride of iron, or a 

 saturated solution of ferric trichloride, in 500 c.c. of water is 

 added to a solution of 20 grams of yellow prussiate of potash in 

 500 c.c. of water. This mixture is allowed to stand for 12 

 hours. The yellow fluid at the surface is then poured off, the 

 remainder filtered and the filtrate washed with distilled water 

 until the washings come through dark blue. Enough water is 

 then added to completely dissolve the precipitate. This should 

 make about a liter of concentrated solution of Berlin blue. 



If a gelatin solution is desired, use from 10 to 20 parts of the 

 Berlin blue solution to one of the gelatin. I usually take 25 

 grams of gelatin to 100 c.c. of water; heat in the same water 

 bath with 200 or 300 c.c. of the Berlin blue solution. When 

 the gelatin solution is melted, add to it, slowly, the Berlin blue 

 solution ; the mixture is then heated until the precipitate, which 

 is usually formed, disappears. Then filter through a flannel. 

 If the mass is to be* kept some time, add a little chloral hydrate. 

 For fish vessels it is best to inject the mass as cool as possible. 



Hoyer's Yellow Lead Chromate Gelatin Jl/ass (see Lee's 

 Vade-Mecum, p. 304) is a ver}' simple mass to make. Prepare 

 2 bottles of stock solution ; in one, make a saturated aqua 

 solution of potassium bichromate, and in the other a saturated 

 solution of lead acetate. Then soak up 25 grams of gelatin in 

 100 c.c. of water; heat to melting point in a water bath; add 

 100 c.c. of the potassium bichromate solution. Afterward heat 

 nearly to the boiling point; add 100 c.c. of the lead acetate 

 solution, and filter throujih a flannel. It is best to make this 



