i 7 8 



A MANUAL OF PHYSIOLOGY 



pointed forceps and freely divided. Connecting the posterior 

 surface of the heart and the pericardium is a slender band of con- 

 nective tissue, the fraenum. A silk ligature may be passed around 

 this with a threaded curved needle, or curved fine-pointed forceps, 

 and tied, and then the fraenum may be divided posterior to the 

 ligature. The anatomical arrangement of the various parts of the 

 heart should now be studied. Note the single ventricle with the 

 bulbus arteriosus, the two auricles, and the sinus venosus, turning 

 the heart over to see the latter by means of the ligature. Observe 

 the whitish crescent at the junction of the sinus venosus and the 

 right auricle (Fig. 74). 



3. The Beat of the Heart. Note that the auricles beat first, and 

 then the ventricle. The ventricle becomes smaller and paler during 

 its systole, and blushes t red during diastole. Count the number of 

 beats of the heart in a minute. Now excise the heart, lifting it by 



means'of the ligature, 

 and taking care to cut 

 wide of the sinus veno- 

 sus. Place the heart 

 in a small porcelain 

 capsule on a little 

 blotting-paper moist- 

 ened with physiologi- 

 cal salt solution.* Ob- 

 serve that it goes on 

 beating. Put a little 

 ice or snow in contact 

 with the heart, and 

 count the number of 

 beats in a minute. The 

 rate is greatly dimin- 

 ished. Now remove 

 the ice and blotting- 

 paper, cover the heart 

 with the salt solution, 

 and heat, noting the 

 temperature with a 

 thermometer. Observe that the heart beats faster and faster as the 

 temperature rises. At 40 C. to 43 C. it stops beating in diastole 

 (heat standstill) . Now at once pour off the heated liquid, and run 

 in some cold salt solution. The heart will begin to beat again. 



4. Cut off the apex of the ventricle a little below the auriculo- 

 ventricular groove. The auricles, with the attached portions of the 

 ventricle, go on beating. The apex does not contract spontaneously, 

 but can be made to beat by stimulating it mechanically (by pricking 

 it with a needle) or electrically. Divide the still contracting portion 

 of the heart by a longitudinal incision. The two halves go on 

 beating. 



5. Heart Tracings. (i) Fasten a myograph-plate (Fig. 75) on a 

 stand. Take a long light lever consisting of a straw or a piece of 

 thin chip, armed at one end with a writing-point of parchment-paper, 

 supported near the other end by a horizontal axis, and pierced not 

 far from the axis by a needle carrying on its point a small piece of 

 cork or a ball of sealing-wax. 



* For frog's tissues this should be 0*7 to 075 per cent, sodium chloride 

 solution, for mammalian tissues a little stronger (about 0*9 per cent.). 



FIG. 74. FROG'S HEART WITH STANNIUS' LIGATURES 

 IN POSITION (CYON). 



Anterior surface of heart shown on the left, pos- 

 terior surface on the right, a, right auricle ; b, left 

 auricle ; c, ventricle ; d, bulbus arteriosus ; e, f, 

 aortas ; #, sinus venosus. 



