AND HOW TO USE IT. 173 



The smaller end is for insertion in the vessel, the con- 

 striction is for the purpose of preventing any slipping of 

 the ligature, over the end of which a short piece of India- 

 rubber tubing is pushed. Make an incision into the coims 

 arteriosus (given off anteriorly and somewhat to the right 

 side from the ventricle) ; place one cannula in it, directed 

 forwards, and tie it firmly in its place. Tie the second, directed 

 outwards, into the sinus venosus ; the third, directed forwards {i.e., 

 towards the dorsal aorta) into the duodenal artery ; the fourth, 

 also directed forwards into the duodenal vein. Fill an ordinary 

 tumbler half-full of plaster of Paris, coloured with a little common 

 "French blue" or ultramarine of the oil-shops. Fill up the 

 tumbler with water, stir well, and immediately strain the liquid 

 through coarse muslin into a second tumbler. Fill the syringe, 

 and inject through all four cannulge successively. This must be 

 done very rapidly, or the plaster will set. On removing the 

 syringe from a cannula, the India-rubber tube should be plugged 

 with a small piece of wood to prevent escape (keep a few pegs 

 ready made which fit well). All the chief vessels are injected in 

 this way : the ventral aorta and its branches from the conus arterio- 

 sus, the systemic veins from the sinus venosus, the dorsal aorta and 

 its branches from the duodenal artery, and the postal vein from 

 the duodenal vein. The caudal and renal postal veins have to be 

 done separately ; the femoral and ilio-hsemorrhoidal veins also 

 often escape being filled. If a preparation for demonstrating 

 purposes be desired, it is advisable to colour the plaster used for 

 injecting the dorsal aorta with vermilion or carmine instead of 

 French blue. 



A Fine Injection for very Small Vessels is made by straining 

 through muslin a strong solution of gum arabic in water coloured 

 with precipitated Prussian blue or carmine. After injection, the 

 subject is placed in alcohol, which coagulates the gum. It has a 

 double advantage over gelatine — that it is used cold and that it 

 keeps better in alcohol. A common brass ear-syringe, holding 

 about two ounces, answers for every purpose, using for cannulas 

 glass tubes as above form, adapted to the nozzle of the syringe 

 with short pieces of caoutchouc tubing. 



