30 ALLEN 
II. TECHNIQUE. 
1. 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. 
floyer’s Yellow Lead Chromate Gelatin Mass (see Lee’s 
Vade-Mecum, p. 304) is a very 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 through a flannel. It is best to make this 
