100 



THE FROG 



CHAP. 



c.art 



A still simpler injecting apparatus is furnished by a common 

 " medicine dropper " (see p. 12, and Fig. 25). By alterna- 

 tive squeezing and releasing the cap, fluid is drawn into or 

 expelled from the tube. 



Having provided these requisites, proceed as follows. 

 Open the abdomen of a freshly- 

 killed frog in the usual way, taking 

 great care not to injure the 

 blood-vessels. Remove the middle 

 portion of the shoulder-girdle, 

 so as to expose the heart, lay 

 open the pericardium, and with 

 the scissors make a snip into 

 the ventricle, allowing the blood to 

 escape freely. Pass a piece of fine 

 thread, about six inches long, round 

 the heart, at about the junction of 

 the auricles and ventricle, and give 

 it a single loose tie, as shown in 

 Fig. 25. When the bleeding has 

 ceased, fill the medicine dropper, or 

 syringe, with injection-mass and 

 pass the riarrow end of the former, 

 or the nozzle of the latter, through 

 the cut end of the ventricle into the 

 conus take care not to push it into 

 one of the auricles instead and 

 tighten the thread so as to keep it in 

 place. Then squeeze the cap of the 

 medicine dropper, or push in the 

 piston of the syringe, and if the 

 operation is successful, you will see 

 the blue injection pass from the 

 conus into the arterial trunks, and 

 thence into the various arteries of 

 the body. The contrast between the 

 arteries, filled with the blue mass, 

 and the veins, filled with blood, is 

 then very striking, particularly in 

 the mesentery. When the arteries 

 are well filled, withdraw the nozzle 

 from the heart and instantly draw 

 the thread tight and knot it so as to prevent escape of the 

 injection. Then place the whole frog in spirit (methylated 

 spirit 3 parts, water i part) for a few hours, after which 

 time the injection-mass will be found to have set hard 



FIG. 25. Sketch showing the 

 method of injecting the 

 Frog's arteries. 

 a. glass "medicine dropper" 

 with india-rubber cap (b) ; 

 its pointed end (dotted) is 

 passed through the cut 

 end of the ventricle (v) 

 into the conus (c. art) ; 

 au. auricular division of 

 the heart ; t. thread. 



