172 INJECTING SMALL ANIMALS FOR 



Do not quite empty the syringe each time, as some air would 

 be forced out with the last of the fluid. Close the stop-cock, 

 refill the syringe and proceed as before, bearing in mind that 

 injecting too rapidly is apt to burst some vessel and spoil the 

 subject. When you think that about sufficient has been forced in, 

 pass a string around the heart and tie it tightly around the canula 

 to prevent further escape ; then force in from one-half to one 

 ounce more, depending on the size of the animal. This is to 

 prevent the capillaries being emptied by the rigor-mortis, which 

 will set in later. (The syringe should be slowly filled, else air will 

 be drawn in at the back and be forced into the animal.) Now 

 close the stop-cock, remove the syringe, and hold the animal in a 

 stream of water from the tap to wash away stains from the outside 

 and the abdominal cavity. It should next be placed for some 

 hours or over-night in ice-water. If desired to harden, ice-cold 

 Miiller's fluid is to be preferred. After which, it may be dissected 

 and the parts desired may be placed in ordinary alcohol. After a 

 few hours this alcohol may be turned off, to be replaced by fresh 

 alcohol. In this way the brain and kidneys will be ready for 

 cutting in forty-eight hours. 



It is a mistake to expect tissues to harden in the second or 

 third alcohol. It is not length of time that is necessary to harden, 

 but the several changes of alcohol to get rid of water from the 

 tissues. 



After hardening, we may cut our sections, place them for a 

 few moments in oil of cloves ; then transfer them one at a time to 

 a clean pad of tissue paper ; put a drop or two of benzole on to a 

 slide ; lay the section into the benzole (which will drive out the 

 air-bubbles) ; apply a drop of Canada balsam, then the cover-glass, 

 and our specimen is ready for the microscope. 



If our balsam has been properly prepared, and the slide is 

 deposited in a warm place, it will soon harden into a permanent 

 mount, to be admired by lovers of the beautiful. 



We cannot well secure the brain and spinal cord by sawing. I 

 find the following to work nicely : — Cut the neck off close to the 

 skull, remove the skin and muscle from the top of the head ; then 

 with a screw-driver or similar tool commence at the foramen 

 magnum ; pick away the skull piece by piece ; this is done by 



