POLYGYRA ALBOLABRIS AND LIMAX MAXIMUS 263 



wholly or till the heart can be plainly seen. The latter method 

 is, I think, preferable, as it avoids the danger of rupturing some 

 of the blood vessels, as sometimes happens when the entire shell 

 is removed. Cut through the peritoneum, alongside the rectum, 

 taking care not to injure the large vein which accompanies the 

 rectum; turn back the walls of the pulmonary cavity till the 

 heart is exposed. Using the curved needle pass a thread under 

 the ventricle. Place the animal in warm water, as hot as can 

 be comfortably borne by the hand, and before injecting be cer- 

 tain that the animal is thoroughly warmed through; also place 

 the syringe in hot water, having both the syringe and injecting 

 fluid warm. Draw some of the fluid into the syringe; then, hold- 

 ing the needle upward, expel a drop or two of the fluid, so as to 

 be certain that no air remains in the syringe. Leaving the animal 

 in warm water, with the point of an extremely sharp scalpel 

 make a slight incision in the walls of the ventricle just large 

 enough for. the point of the needle to enter. Insert the needle, 

 bring the two ends of the thread together and tie them just back 

 of the point of the needle, to guard against the escape of the 

 injection through the incision. Some assistance would be useful 

 in this operation, as one hand will be occupied with the syringe. 

 Gently press the piston, slowly injecting the fluid, stopping im- 

 mediately when the injection is complete, as much pressure will 

 rupture the walls of the blood vessels. 



Sometimes a very fine injection of the arteries can be made 

 by merely inserting the point of a hypodermic needle in the ven- 

 tricle, the rest of the process being as described above. But the 

 injection is liable to escape where the needle enters the wall of 

 the ventricle. 



The injecting is a very delicate process, and partial, or even 

 a complete failure at the first attempt should not discourage the 

 student. The most frequent cause of failure is in not keeping the 

 animal and syringe warm enough, the injecting fluid rapidly hard- 

 ening in the blood vessels, preventing their full injection. 



When the animal is fully injected, place it at once in cold 

 water; this rapidly hardens the gelatin. The remainder of the 



