APPENDIX. 485 



C. ON INJECTING. 



I. Precautions, indispensable to success under all circum- 

 stances. 



a. Injection should always be performed as soon after 

 death as possible ; and, in the case of the Frog, 

 it is advisable to first remove the apex of the ven- 

 tricle, in order to allow of the escape of as much 

 blood as possible. 



b. In filling the syringe (or its equivalent) with injecting 

 material care should be taken to first expel the con- 

 tained air : when fully charged it should be held 

 nozzle uppermost, while, by displacement of the 

 piston, all trace of air is dispelled. 



c. In opening a blood-vessel prior to injection the 

 exposed wall should be slit longitudinally with small 

 scissors. Escape of as much blood as possible 

 should be permitted. Before inserting the cannula 

 or its equivalent, the whole should be well washed 

 and the incision examined to make sure of the ab- 

 sence of a blood-clot or other obstructive agent. 



To this end the introduction of the cannula may 

 be advantageously preceded by that of the seeker. 



d. If the cannula is to be tied in place (as must always 

 be the case when injecting for histological purposes) 

 the thread (preferably one of surgical silk) should be 

 passed round the vessel and loosely knotted, prior to 

 making the incision in its wall. The incision should 

 be made a short distance from the thread, in a 

 direction away from that in which it is intended to 

 inject. 



Under such circumstances the knotted thread will 

 be found to serve as a landmark, which experience 

 will show to be occasionally necessitated, in the 

 course of the work. 



