AND HOW TO USE IT. 177 



branches may be traced into the foot and to many other parts 

 which were considered to be destitute of arteries.* 



Injecting Fishes. — It is difficult or quite impossible to tie the 

 pipe in the vessel of a small fish. If we inject from the heart, the 

 fluid passes through the gills. The best way is to cut off the tail 

 of the fish, introduce the pipe into the divided vessel which lies 

 immediately beneath the spinal column. In this manner beautiful 

 preparations may be made. 



Double Injection of the Eye and Spleen.— It is well to drive 

 the injection mixture intended for the venous system through the 

 artery first, and then through the same vessel the second mass 

 which is to serve for the arterial system. Not unfrequently the 

 injection may be essentially regulated by keeping open or closing 

 the terminal vein. The beginner often experiences a difficulty in 

 finding the vessel from which to inject ; and to distinguish the 

 arteries from the veins. This may be found by making a longitu- 

 dinal incision in the vessel, and with a blunt, thick needle probing 

 a little distance into the tube. The artery will be found thicker in 

 the coating than the vein, and the difference is easily perceived by 

 this mode of testing. The vein is also of a bluer colour than the 

 artery. 



A sheep's foot injected forms a good object. The liquid 

 should be forced into it until a slight paring of the hoof shows the 

 colour in the fine channels there. The tongue of a cat is also a 

 very beautiful injection. A solution of tannin, injected after 

 washing with warm water, renders arteries impervious to the 

 coloured fluid afterwards thrown in. A little practice will enable 

 the beginner to overcome the difficulties of injection. A few 

 failures may be expected at first, but after three or four trials per- 

 fection will soon be gained. Careful dissection and attention to 

 the directions here laid down will save much labour and loss of 

 time. The injection of single organs— as liver, lung, etc. — will be 

 treated of under the preparation of the same in a future part. 



Injecting Annelids. — For annelids with dark tissues, like 

 Hintdo, a light-coloured (white or yellow) injection-mass should 



* On "The Orgnns of Circulation of Helix Poniatia," Aiinah aiid Maga- 

 zine of Natural History, Jan., 1867. 



Vol. VI. N 



