414 EXPERIMENTAL PHARMACOLOGY 



is desirable to prolong the later stages as much as possible 

 to bring out the action of the drug well. 



When marked slowing is present (vagus center stimu- 

 lated) the blood-pressure may be considerably lowered. 

 After a time irregular heart beats appear and the elevation 

 of the pressure varies from moment to moment. Watch 

 carefully now, for great irregularity of the heart may sud- 

 denly appear at any time, i.e., the vagus may lose control 

 of the heart whose muscle fibers become so irritable that 

 the organ breaks loose from the inhibition and begins to 

 beat very rapidly, and irregularities, extra systoles, etc., 

 soon appear. When this very rapicl (3rd) stage appears 

 the pressure may continue high for a little while but de- 

 lirium cordis (fibrillation) is likely to appear at any mo- 

 ment. When it does the pressure will fall to zero at once, 

 perhaps from a considerable height. The respiration will 

 stop at about the same time as a rule. Watch carefully for 

 the animal to die, and as soon as the pressure suddenly 

 falls to zero (and remains there) open the chest quickly 

 with large tinner's snips and observe the condition of the 

 heart. It should be fibrillating. Are the chambers in sys- 

 tole or diastole. Place your hand on the heart and note the 

 character of the movements. How long does the fibrilla- 

 tion last? Can you determine the three stages of the drug's 

 action on the heart as shown by your record ? What con- 

 clusions can you draw from the experiment ? How much 

 drug is required to kill the animal? Could you assay the 

 strength of an unknown preparation of digitalis by compar- 

 ing the size of the lethal dose of the preparation with the 

 size of the fatal dose of a standardized preparation? On 

 this basis a number of methods for assaying the strength 

 of preparations of digitalis and related bodies have been 

 proposed. (For literature, see Houghton, E. M. : The 

 Lancet, 1909, June 19; Hatcher and Brody: Journal of 

 Pharmacology, 1910, August, p. 362 ; Famulener and Lyons r 

 Proceedings of the American Pharmaceutical Association, 



