OF THE CALABAR BEAN. 

 A = diameter of a small artery ; B = diameter of a very small vein. 



767 



Time. 



A. 



B. 



Notes. 



15 minutes before 



poisoning, 

 10 Do. 



l 5-0 

 50 



3-0 

 3-0 





5 Do. 



5-0 



30 



Two grains of extract, in fifteen minims of 



Time after Administra- 







tion of Poison. 







water, were injected into the left flank. 



5 minutes, 



5 



30 





10 „ 



47 



3-0 



Circulation oscillating. 



15 



42 



30 





20 „ 



4-2 



2-9 





25 



4-0 



2-9 





28 „ 



49 



30 





29 „ 



5-7 



30 





30 



60 



3 2 



Stasis, and crowded vessels. 



35 „ 



7-0 



3-5 



Slow circulation. 



40 „ 



7 



3-5 





45 „ 



80 



35 



Faint oscillations. 



50 



8-0 



35 





1 hour, 



80 



3-5 





2 hours, 



8-0 



3-5 





The action of Calabar bean on the minute blood-vessels of the frog's web is, 

 therefore, to contract them considerably first, and then dilate them. The con- 

 traction may be influenced, to a slight extent, by the reduction in the frequency 

 of the heart's action ; but the succeeding dilatation, during a still greater reduc- 

 tion, would lead us to suppose that it is mainly due to a specific effect on the 

 ganglia and nerves that govern the calibre-changes of the vascular system, because 

 it is by their influence that the final dilatation must be produced. 



We are now in a position to explain the changes of blood tension that have 

 been described in mammalians. The slight fall that usually occurs in the 

 mean pressure immediately after the poison has been exhibited, I believe to be 

 solely due to the diminution in the rate of the heart's contractions, which has 

 always been caused by that time. The subsequent rise in both arterial and 

 venous tensions before any considerable embarrassment of the respiration, may 

 be satisfactorily explained by such contraction of the smaller arteries and 

 veins as has been demonstrated to occur in the vessels of the frog's web. 

 It cannot be caused by increased cardiac pressure ; for the heart is at the time 

 contracting with only one half its normal rapidity, or with even less ; while the 

 greater force of each heart beat the increased oscillating distances appear to indi- 

 cate, is quite insufficient to account for the high degree of blood tension some- 

 times attained. The subsequent, more or less rapid diminution of pressure in 

 both arterial and venous systems is the evident result of the great dilatation in 

 the minute blood-vessels, assisted by the weakening of the vis e tergo that this 

 poison quickly produces. 



VOL. XXIV. PART III. 9 Y 



