THE BLOOD VESSELS 
i°5 
the leg and the body, where it lies superficially beside the some¬ 
what smaller femoral artery. A ligature should be passed around 
the vein and its accompanying artery separately before the 
injection is begun. Insert the cannula by the method above 
described (p. 103) through an incision in the wall of the vein 
distal to the ligature, and inject toward the heart, i.e., in the 
direction of normal blood flow. The injection mass will thus fill 
the veins along the whole course from the point of injection to the 
heart and will, moreover, back into the other branches of the 
posterior vena cava and into the anterior vena cava until it meets 
the first valves guarding these. It will also go forward through 
the heart and fill the pulmonary artery and its branches. If the 
injection is not successful, the other femoral artery may be tried, 
or in the case of a small animal the injection may be made much 
more readily through one of the jugular veins in the neck region. 
2. Systemic Arteries and Pulmonary Veins with Red. 
Here again unless the animal is too small, the injection may be 
made from the femoral region through the femoral artery, and will, 
if successful, fill not only the whole arterial system (as will be seen 
by watching the progress of the injection mass in the numerous 
small arteries of the mesentery), but will force its way past the 
bicuspid valve of the heart and back into the pulmonary veins. 
In case the animal is too small for ready injection through the 
femoral artery, inject through the left ventricle directly through 
a puncture made through the thick ventricular wall by means of 
the cannula. If a plug of cotton is inserted as the cannula is 
withdrawn, the puncture may be successfully closed, though the 
elasticity of the thick muscular wall itself will usually accomplish 
this closure. 
3. Hepatic Portal System with Yellow. 
This injection may be made through any convenient mesenteric 
vein. If one place fails, clamp it and try another. Close by 
clamp or by temporary pressure of a wad of wet absorbent cotton, 
or by the finger. 
After injecting, cool the specimen under the cold water faucet, 
to harden the gelatine. Make a slit in the wall of the stomach and 
