242 THE MICROSCOPE. 



pipe \vould necessarily be forced into the vessels, and the 

 injection would fail. 



" The point of the pipe can with very little trouble be 

 made to enter the artery. The needle with the thread is 

 next carried round the vessel and the thread seized with 

 forceps, the needle unthreaded and withdrawn, or one end 

 of the thread may be held firmly, while the needle is with- 

 drawn over it in the opposite direction. The thread is 

 now tied over the vessel, so as to include the tip of the 

 pipe only, for if the pipe be tied too far up, there is greater 

 danger of its point passing through the delicate coats of 

 the vessel. 



" The nozzle of the syringe, which has been well washed 

 in warm water, is now plunged beneath the surface of the 

 fluid, the piston moved up and down two or three times, 

 so as to force out the air completely, and the syringe 

 filled with fluid. It is then connected with the pipe, which 

 is firmly held by the finger and thumb of the left hand, 

 with a screwing movement, a little of the injection being 

 first forced into the wide part of the pipe so as to prevent 

 the possibility of any air being included. 



" The pipe and syringe being still held with the left hand, 

 the piston is slowly and gently forced down with a slightly 

 screwing movement with the right, care being taken not 

 to distend the vessel so as to endanger rupture of its 

 coats. The handle of the syringe is to be kept uppermost, 

 and the syringe should never be completely emptied, in 

 case of a little air remaining, which would thus be 

 forced into the vessels. The injection is now observed 

 running into the smaller vessels in different parts of the 

 organism. 



" I will now proceed to inject the ox-eye in the same 

 manner. The pipe is inserted into this branch of artery 

 close to the nerve. Two minutes will probably be suffi- 

 cient to ensure a complete injection. In making an 

 injection of the eye, if the globe becomes very much 

 distended by the entrance of the injecting fluid, an opening 

 may be made in the cornea to allow the escape of the 

 aqueous fluid which will leave room for the entrance of 

 the injection, and permit the complete distension of the 

 vessels. 



