374 THE AMERICAN NATURALIST.. [Vor. XXXIX. 
Thus, the starch and the color were added both at once. In the 
absence of the prepared starch mixture, a similar result may be 
attained as follows. 
Mix together some of the grocer’s pulverized cornstarch and 
about one seventh its volume of a suitable finely powdered col- 
oring matter (carmine, insoluble Prussian blue, chrome yellow, 
chrome green). Add a little cold water to the mixture and con- 
vert it into a thick paste. Into the melted gelatin stir one third 
or one fourth its volume of the colored starch paste. The pro- 
portions of the mixture may be varied, as occasions demand. I 
have found the following formula convenient : — 
Melted gelatin i | ; ; : . . 75 volumes. 
Dry cornstarch . : ; : i QU > us 
Dry color. : ee ; Saag 
For non-histological purposes it is, of course, unnecessary to 
use the finer grades of gelatin, such as photographic gelatin. 
Any ordinary culinary gelatin serves equally well, besides being 
always easily obtainable and less expensive. A mass of good 
stiffness for injection purposes is obtained by using 1 gram of 
dry gelatin to every 7 or 8 ccm. of water. If the vessels to be 
injected contain much blood, the gelatin solution must be of 
such strength that the mingling of the blood with it will not 
prevent the hardening of thé mass. It is better not to inject 
the veins of a skate immediately after the death of the animal, 
for then the sinuses contain a large quantity of blood. If the 
fish is kept in a cool place for about two days after death, the 
greater part of the blood will have disappeared from the vessels. 
At the same time, the walls of the vessels will have relaxed so 
that the injection is more likely to pass into the smaller vessels. 
This latter consideration is of more importance with reference 
to the arteries than to the veins. 
As regards the convenience of the starch-gelatin method, the 
warming of the animal, preliminary to the injection, is unnec- 
essary. The chief difficulty, therefore, which attends the gela- 
tin method as ordinarily used for histological purposes, is 
obviated. I have obtained good starch-gelatin injections of the 
entire circulatory system of the skate, working in a room at 
