504 APPENDIX 



Tie a piece of the thinnest rubber dam over the top of the arm of the 

 oncometer, and fill it with Ringer's fluid (consisting of a weak solution 

 of sodium and potassium chlorides and of basic calcium phosphate in 

 distilled water). Remove a large frog's heart by cutting it transversely 

 with the scissors about midway through the auricles. With a moistened 

 fine silk thread tie the heart over the end of the perfusion cannula so that 

 the latter shall extend just into the ventricle through the auriculo- 

 ventricular opening, and be sure that the openings of the cannula are not 

 obstructed; Press the cork of the cannula into the body of the oncometer 

 and adjust , if necessary, so that the heart shall hang free in the surround- 

 ing solution, being sure that the instrument contains no bubble of air. 

 Fill the portion of the inflow-tube above the closed clamp with the solution, 

 and insert the short arm of the siphon in the Ringer's fluid in the beaker 

 above. Adjust to the rubber diaphragm the tiny cork block and above it 

 the light straw lever attached to the cork stopper by a crank-shaped pin. 

 Now loosen the pinch-cock slightly to allow the solution to run slowly 

 down the tube. Gradually raise the upper beaker in the stand-ring. 

 When the pressure has reached that of 10 or 15 cm. of water the ventricle 

 will begin to beat rhythmically. If not, insert fine copper wires in the 

 oncometer and connect them with a dry-cell through a key. It is some- 

 times impossible to obtain frog-hearts large enough for this experiment; 

 it is difficult to insert the perfusion-cannula into the ventricle of a small 

 frog-heart without obstructing the former. 



Only in very recent years has the extreme importance of the salines 

 in the blood become apparent, but calcium, magnesium, sodium, potas- 

 sium, etc., are now known to be important in the composition of proto- 

 plasm. Deprived of their continual supply of these metals by way of 

 the blood, tissues promptly cease to function, while, on the other hand, 

 an isolated heart even of a mammal may be made to beat for hours when 

 perfused with these salines in the proper proportions and kept warm 

 and moist. We are still only at the gate-way of the physiology of the 

 inorganic salts in protoplasm. Perhaps the ions are the real causes of 

 this complex influence of the various saline substances. 



Expt. 68. The Refractory Period, Extra Contraction, and Compensatory 

 Pause. (Apparatus: Kymograph, etc., heart-lever, inductorium, heart.) 

 Place the normal heart in the heart-lever and arrange the latter to write 

 on the drum rotating at a slow speed. Run wires to the heart from the 

 inductorium's secondary coil. Record the normal beat of the heart on 

 the drum. Early in the uprise of the lever at some beat throw into the 

 heart a maximal make induction-shock (cutting out the break). By 

 stimulation within this period no extra contraction is produced. This 

 (the period of systole approximately) is the "refractory period" of the 

 heart. Throw in another maximal make-shock just at the height of 

 the lever's rise; the stimulation now causes an extra beat. This is 

 the "extra contraction" Now observe that the next automatic beat 

 does not occur at the time in the regular rhythm when it should, but that 

 there is a pause of the heart until the time of the succeeding regular beat. 



