CIRCULATION OF THE BLOOD. 



peared and then bathe the heart in a o.2-per-cent solution of atro- 

 pine sulphate, first confining the application of the drug, so far as 

 possible, to the sinus venosus. Is the heart-beat altered in any 

 way? 



Now repeat the stimulation of the nerve. What is the effect on 

 the heart-beat? Is there acceleration or inhibition? Compare 

 this with the tracing obtained before the application of the drug. 



Stimulate the vagus at the sinus. Is any inhibitory effect pro- 

 duced ? What effect, then, has atropine upon the extrinsic nervous 

 mechanism of the heart ? 



Continue the application of the drug until its effect upon the 

 heart muscle becomes manifest. Wash repeatedly with physiolog- 

 ical salt solution. Does the heart recover from the effects of the 

 atropine ? Repeat the stimulation of the nerve. Is inhibition again 

 finally brought about ? 



2. Cocaine. If the heart used in experiment i has recov- 

 ered it may be used again for this experiment. Otherwise, a new 

 preparation will have to be made. 



The heart is arranged for recording as before and the vagus 

 nerve, for stimulation. A control tracing is made of the heart-beat 

 with and without stimulation of the nerve. 



While the tracing is being taken, allow a few drops of a 0.2-per- 

 cent solution of cocaine in o.6-per-cent salt solution to fall upon 

 the heart. Note the effect upon the heart-beat. Is there any dis- 

 turbance of co-ordination ? 



After any irregularity in the beat that may have occurred has 

 disappeared, stimulate the vago-sympathetic nerve. Is any inhib- 

 itory effect produced ? 



Continue the application of the cocaine solution until the ven- 

 tricle ceases to beat. Note the changes in the heart's action as the 

 cocaine effect is continued and increased. 



3. Pilocarpine. In a pithed frog, make a heart prepara- 

 tion for recording, and expose the vago-sympathetic nerve for 

 stimulating. Take first a tracing of the beat before the addition 

 of the drug. Make another tracing during stimulation of the nerve 



