THE CIRCULATION OF THE BLOOD 101 



3. Observations. Trace a plethysmogram while holding the 

 limb as still as possible. Breathe regularly and deeply. 



(1) Are the cardiac contractions visible in the tracings; and, if so, 

 does the part get larger or smaller in cardiac systole? 



(2) Are the respiratory movements evident; and, if so, does the 

 part get larger or smaller during inspiration. Account for results. 



(3) While the arm is enclosed in the plethysmograph, slowly con- 

 tract the flexor muscles of the forearm. Does the volume increase 

 or diminish on contraction? Account for results. 



XIII. THE ACTION OF ATROPINE UPON THE HEART. 



1. Material. Two dogs; atropine sulphate; morphine sulphate; 

 chloroform (or ether); mask. 



2. Preparation. Make up following solutions: a strong solution 

 of atropine, 0.4 grm. to 10 c.c.; morphine, 0.6 grm. to 10 c.c. Simply 

 restrain dog "a." Fasten dog "6" to board. Give hypodermically 

 0.03 grm. of morphine to dog "b," then anaesthetize him. Set up 

 inductorium so as to obtain tetanizing current. 



3. Experiments and Observations. (1) Expose the vagus of 

 dog "b." Stimulate it with weak induced current, using shielded 

 electrode. 



(2) Count the pulse; then give 5 mg. atropine hypodermically. 



(a) Count the pulse at short intervals after the injection of atropine 

 for at least thirty minutes, or until its rate is markedly affected. 



(b) What is the effect of atropine on the rate of the pulse ? Could 

 atropine produce this effect by acting on the vagus centre ? On the 

 vagus fibres? On the heart muscle direct? 



(3) After the pulse rate has been markedly affected by atropine, 

 stimulate vagus as before, using shielded electrodes. 



(a) What is the effect on the rate of the heart's action? 



(6) Compare this result with that obtained in experiment (2). 



(c) Had atropine acted solely by depressing the vagus centre, would 

 we have found a difference in results in stimulating the vagus nerve 

 before and after its exhibition? 



(d) Had atropine acted on the accelerator apparatus, would there 

 be a difference in such results? 



(e) If now, on stimulating the heart muscle directly, you obtained 

 a normal physiological effect, to what elements have you limited the 

 possible action of atropine? 



(/) Basing your opinion on the experiments you have performed, 

 to what elements have you limited the possible action of atropine? 



(4) Further general observations. 



(a) Note condition of visible mucous membranes with regard to 

 their secretions. 



(b) If dog can be kept until next day, note size of pupils. 



