ADVANCED EXPERIMENTAL PHYSIOLOGY 151 



of curarised frogs with intact circulation, and also in the gal vanome trie 

 records of the action current of nerve. Waller attributes the staircase 

 effect to the influence of C0. 2 formed 'by the katabolism of the active 

 tissue. 



FIG. 152. Stanniused heart. Summation of stimuli. A, ineffective, and B, 

 effective stimuli. The time is marked in seconds. (L.H.) 



Summation of Stimuli. Pull out the secondary coil until the break 

 shock is just ineffective, and rhythmically stimulate the Stannius pre- 

 paration with this inadequate stimulus. The heart will respond to the 

 repeated excitation, and the first few beats will show the staircase 

 phenomenon. 



CHAPTER XXXVI. (Advanced). 

 THE HEART-CoNTiMJED. THE ACTION OF DRUGS. 



The Suspension Method of Investigating the Action of Druis on the 

 Frog's Heart. Large frogs and great care are necessary for this 

 experiment. Pass a ligature under the vena cava inferior, where it is 

 joined by the hepatic veins and enters the sinus. Make a V-shaped 

 incision, and tie in a fine glass cannula. The cannula must be provided 

 with a rubber tube ending in a syphon tube. The tube is provided 

 with a clip, and the whole is filled with Ringer's solution, which is 

 contained in a flask. Attach a hook to the ventricle apex, and record 

 the heart by the suspension method. A slit is made into the aorta. 

 Open the clip, circulate the Ringer's fluid, and record a series of 

 contractions. Now replace the flask of Ringer's solution with one 

 containing distilled water. 



1. 0*75 % NaCl solution in distilled water followed by a Ringer or 

 Locke's solutions until the normal beat is recovered. 



