378 THE AMERICAN NATURALIST. [Vor. XXXIX. 
Systemic. 
6. Lateral --------- forward - - - blue starch-gelatin. 
c UM Gone ehe nece backward +; 9 E " 
Renal Portal. 
8. Caudal----------- forward -- yellow starch-gelatin or starch. 
If it is desired to use gelatin for only the systemic veins, where 
it is of greatest advantage, the arteries and the two portal 
systems may first be injected with cold starch and then the 
systemic veins with gelatin alone, for it is unnecessary to add 
starch to the gelatin to prevent its passing capillaries when all 
of the vessels beyond the system which is being injected are 
already filled. 
Are so many as eight separate injections necessary? My 
experience has been that to decrease the number of operations 
is to increase their difficulty and to render the results less satis- 
factory. A mass injected into the systemic veins may pass 
through the heart into the afferent branchial vessels. Yet I 
have found it difficult to secure a full injection of the finer 
afferent vessels of the gills except by injecting directly into the 
ventral aorta itself. A perfectly fluid mass injected into the 
hepatic portal vessels or into the caudal vein may be made to 
fill the greater part of the venous system. But it is a great 
advantage in the dissection to have the hepatic portal and renal 
portal vessels distinguished from the systemic veins by a differ- 
ent color. The difference in color serves to emphasize to the 
mind of the student in a forcible way the nature of the relation 
between the portal systems and the systemic veins. The sim- 
plest way of securing the color difference is to inject each portal 
system separately. All the systemic arteries may be injected 
from the caudal artery at a single operation, but students suc- 
ceed better with the two-way injection at the anterior mesenteric 
artery. In short, it is better to make eight easy operations than 
to make two or three of greater difficulty and less certainty. 
