612 



ON THE PHYSIOLOGICAL ACTION OF CASCA BAEK. 



In this experiment, as well as in several others, the blood- 

 pressure rose without being accompanied by a slowing of the 

 pulse, and this indicates that the latter is not dependent on the 

 former. 



The excitability of the vagus-roots to reflex stimuli does not 

 seem to be increased by casca, as a stimulus of the same 

 strength applied to the central end of one vagus had a similar 

 effect before and after the injection of the drug. We would 

 call attention, however, to the very extraordinary effect which 

 succeeded the application of a stronger stimulus, an ejffect which 

 seems all the more extraordinary from occurring after the 

 stimulus had ceased, and not during its application. 



Irritation of the vagus-roots by the carbonic acid accumu- 

 lated in the blood during the tetanic inspiration, which lasted 

 during the irritation, at once suggests itself as a cause of the 

 slow pulse which followed the irritation ; but the fact that the 

 pulse was not affected when the distance of the coil was 10 cm., 

 although the thorax was tetanically expanded, seems to indicate 

 that the slowing which followed the stronger irritation from a 

 secondary coil at 8 or 6 cm. distance from the primary was due 

 to reflex action, which the first irritation had been too weak to 

 produce. 



From Experiment XXXV it will be seen that after the 

 administration of a large dose of casca, irritation of the vagi, 

 instead of producing slowing or stoppage of the heart's action, 

 increased the frequency of its pulsations. The acceleration 



