74 SPECIAL PHYSIOLOGY 



(4) Do the corpuscles change shape? If so; under what circum- 

 stances ? 



(5) Enumerate all the observed structural and functional features 

 which differentiate arterioles from venules. 



B. To Observe the Action of the Frog's Heart. 



1. Preparation. After the capillary circulation has been observed, 

 the frog may be pithed and stretched upon a cork board, ventrum 

 up. Make a median incision through the skin from the pelvis to 

 the mandible; make transverse incisions and pin out the flaps. 

 Raise the posterior cartilaginous tip of the sternum; insert a blade 

 of the fine scissors under it and divide it transversely, about J cm. 

 anterior to the tip. Raise the anterior segment of the sternum at 

 the point of the transverse incision; insert the blade of the strong 

 scissors under it and divide it longitudinally in the median line. 

 Withdraw from the board the pins which fix the anterior extrem- 

 ities; make gentle lateral traction upon the fore-feet until the slit 

 sternum is sufficiently separated to afford a convenient working 

 distance and to expose the whole heart. 



2. Observations. (1) Note rate of systole. 



(2) Note sequence of contraction of auricles, ventricles, and bulbus. 



(3) Note change in shape of different parts. 



(4) Note the change in color and the position of the different 

 parts of the heart during the cycle of changes that come with each 

 heart beat. 



(5) Carefully excise the heart, including the sinus venosus and 

 the bases of the posterior and two anterior vense cavae, also the 

 bases of the two aortic trunks. Place the excised heart in a watch- 

 glass. Observe whether the pulsation continues. If so, what is 

 your conclusion regarding the relation of the heart movements to 

 the central nervous system? 



(6) If the pulsation continues, note whether or not the rate of 

 pulsation has been notably changed by the excision. 



(7) Bathe the heart with a few drops of normal solution. Note 

 any change in the rate of the beat. 



(8) Hold the watch-glass in the palm of the hand and note whether 

 there is any change in the rate of the beat. 



(9) Float the watch-glass on ice-water and note any resulting 

 modification of rate. 



(10) If the heart seems vigorous (otherwise procure a fresh one), 

 carefully sever the sinus venosus with the fine scissors. Does the 

 sinus continue to beat? Does the heart continue to beat? Inter- 

 pretation. 



(11) If the heart beats, sever the auricle from the ventricle through 

 the auriculo-ventricular groove. Note results. 



