CHAPTER XXI 



PERFUSION OF VESSELS. LYMPH-HEARTS 



Estimation of contraction or dilatation of vessels by measurement 

 of perfusion rate. Tie a small glass cannula, bent round so that its 

 limbs are parallel, into the aorta of a large frog killed by destruction 

 of the nervous system ; it can either be passed directly into the cut 

 aorta or more easily through an incision in the ventricle. 



In exposing the heart and aorta make as small an opening as possible. First 

 remove a flap of skin, then cut through the upper part of the ensiform cartilage 

 and extend the incision on either side of the sternum : force this up like a flap 

 until the heart is sufficiently exposed. 



The cannula must be filled with Ringer's solution, and connected 

 through an india-rubber tube with a reservoir of the same fluid so 

 that the fluid is slowly dropping from it during its introduction; 

 this is for the sake of excluding air bubbles. 



Suspend the frog by a pin through the jaw, and fix the reservoir a 

 short distance above the head so that the fluid flows into the vessels 

 by gravitation. Make a cut into the sinus venosus to enable the fluid 

 to flow freely out after it has traversed the blood-vessels of the body ; 

 the escaping fluid will drop from the toes, which should be tied together. 

 A cut must also be made through the skin of each foot to prevent any 

 accumulation in the lymph-spaces of the legs. Count the number of 

 drops per minute, and repeat the counting twice ; after the blood 

 is completely washed out the flow should be fairly regular. 



To test the effect of drugs or reagents upon the muscular tissue of 

 the arterioles the reagent is added in known quantity to the perfused 

 fluid. The Ringer's fluid to which the drug is to be added is placed 

 in a second reservoir as in perfusion of the frog heart (see fig. 61, p. 70). 

 Again count the number of drops per minute (3 estimations), and 

 thus determine whether the arterioles are becoming dilated or con- 

 tracted as the effect of the reagent. This experiment may be tried 



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