ACTION ON ARTERIOLES AND VASO-MOTOR CENTRE. 



515 



was followed by reaction, which did not exceed the original 

 rapidity of the circulation. No dilatation or contraction of the 

 vessels w^as seen to accompany the original slowing. 



Although the results of experiments on the frog's web gave 

 no definite information regarding the contraction of the arterioles 

 under the influence of casca, yet no reasonable doubt can be 

 entertained that in mammals they do contract ; for this is the 

 only possible explanation of the exceedingly slow fall of the 

 blood-pressure during the intervals between the beats of the 

 heart when these have become slow, either from the action of the 

 drug or from irritation of the vagus-trunk. {Of. antea, p. 143.) 



In order to ascertain whether this contraction was due to the 

 action of the drug upon the vasomotor centre in the medulla 

 oblongata or in the vessels themselves, the vasomotor centre in 

 the medulla was separated from its connection with the vessels 

 by division of the spinal cord in the neck previous to the injec- 

 tion of casca. 



Effect on Blood-pressure after Division of Cord. 



Experiment XLII. — May 17. 



A large strong cat, weighing 7i lbs., was chloroformed. A 

 cannula was inserted into the left carotid., and another into the 

 jugular vein. The spinal cord was then divided opposite the 

 second cervical vertebra, and artificial respiration kept up. 



Time. 



Condition after section of cord and pre- 

 vious to injection of casca 



Injected 1 c.c. watery solution of casca 



Oscilla- 

 tions. 



mm. 

 5 



5 



12 



20 



25 



12 



5 



4 



3 



2 L 2 



