194 THE CIRCULATION OF THE BLOOD AND LVMPti 



which is in the field of the microscope, using a fine pipette. Observe 

 the process of inflammation, including stasis and diapedesis (p. 61). 



2. Anatomy of the Frog's Heart. Expose the heart of a pithed frog 

 by pinching up the skin over the abdomen in the middle line, dividing 

 it with scissors up to the lower jaw, and then cutting through the 

 abdominal muscles and the bony pectoral girdle. The external ab- 

 dominal vein, which will be observed on reflecting the skin, can be 

 easily avoided. The heart ^yill now be seen enclosed in a thin mem- 

 brane, the pericardium, which should be grasped with fine-pointed 

 forceps and freely divided. Connecting the posterior surface of the 

 heart and the pericardium is a slender band of connective tissue, the 

 fraenum. A silk ligature may be passed round 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. 86). 



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 

 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 tak- 

 ing care to cut wide of the 

 sinus venosus. Place the 

 heart in a small porce- 

 lain capsule on a little 

 blotting - paper moist - 

 ened with physiological 

 salt solution.* Observe 

 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 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. 87) on a 

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



* For frog's tissues this should be 0-7 to 0-75 per cent, sodium chloride 

 solution, for mammalian tissues a little stronger (about 0-9 per aent.). 



Fig. 86. Frog's Heart with Stannius* ligatures in 

 Position (Cyon). Anterior surface of heart shown 

 on the left, posterior surface on the right, a, right 

 auricle; 6, left auricle; c, ventricle; d, bulbus arte- 

 riosus; e, f, aortae; g, sinus venosus. 



