No. 462) THE SKATE FOR ANATOMICAL STUDY. 373 
make the two-way injection of it usually less difficult to the stu- 
dent than the single injection of the duodenal vein. 
Injection Masses.— For the injection of the vessels of the 
skate I have used an injection mass which is merely a slight 
modification of well known masses, but one which may be found 
to possess peculiar virtues for certain special purposes. Among 
the injection masses suitable for purposes of gross dissection, 
the cold or unboiled starch mass of Pansch ('77, '81; see Whit- 
man, ’85, pp. 223-225) is doubtless best for general laboratory 
use, especially where, in the case of a large class, many injec- 
tions must be made rapidly. It is inexpensive, easy to use, and 
gives results satisfactory for temporary demonstrations. It is, 
however, not perfectly adapted for permanent demonstrations or 
museum preparations, owing to the fact that it does not “ set" or 
harden. The particles of starch remain in a discrete condition 
so that, in the event of any injury to the wall of an injected ves- 
sel, the mass may leak out and discolor the surrounding tissue. 
The starch mass is poorly adapted for the injection of the ven- - 
ous system of the skate because it is practically impossible, to ` 
dissect the thin-walled and irregularly shaped vessels without an 
occasional slight injury, which gives rise to annoying leakage of 
the mass. 
Recently I had need of a mass which should acquire, after 
injection, a fairly stiff consistency without becoming brittle, 
which should not pass through capillaries, and which should 
be convenient to use. Some modification of the gelatin method 
seemed most likely to satisfy these conditions. A gelatin mass 
with the coloring matter in solution, as ordinarily prepared, is 
designed to pass capillaries. After some unsatisfactory experi- 
ments with gelatin colored by means of pulverized carmine or 
insoluble Prussian blue in suspension, it was suggested by Mr. 
J. A. Long, who was working with me, that starch be mixed 
with the melted gelatin to prevent its passing into the capillary 
vessels. We had at hand a supply of the unboiled starch mix- 
ture in several colors. The method which we used with success 
at that time consisted in stirring into the melted gelatin about 
one fourth its volume of the thick starch mass, which always 
settles to the bottom of a jar containing the raw starch mixture. 
