OF THE CALABAR BEAN. 765 



tion with the heart. The action on the frequency of the heart's beats is well illus- 

 trated in this experiment ; from their number having been considerably increased 

 before the exhibition of the poison, by the division of the vagi nerves. 



The distance over which the mercury travels in the oscillating column seems 

 to be increased as the effects of the poison manifest themselves. This appears 

 from all the experiments in this series, but especially from the second and the 

 last. The division of the vagi, in the last experiment, had abnormally diminished 

 the distance of oscillation ; and, yet, it became much greater after the poisoning 

 than it had been previous to the nerve-division. It further appears that this 

 increase in the oscillating distance occurs when the arterial tension is about its 

 maximum. It can only be explained by a very decided increase in the force of 

 the cardiac contractions. I believe that this effect on the heart is altogether a 

 reflex one, due to the resistance to the propulsion of the blood, that the augmen- 

 tation in the general vascular tension must excite. In a normal condition, a 

 stimulus of this nature might be expected to operate by increasing the number 

 and not the strength of the cardiac contractions ; but any tendency to increased 

 frequency is opposed by the action of physostigma, for we have already seen that 

 this substance diminishes the number of the contractions, by prolonging the 

 diastolic pause. Their strength may, however, continue unchanged ; and, during 

 the operation of physostigma, a stimulus may even increase it without affecting 

 the number of the beats, so long as the ganglia that initiate the systolic contrac- 

 tion have their excitability merely lowered without being destroyed and the con- 

 tractile power of the cardiac muscle continues undiminished. 



Before discussing any further the changes of blood tension, it will be advisable 

 to examine the condition of the minute blood-vessels during the action of physos- 

 tigma. 



2. Examination of the Calibre-Changes in the smaller Blood -Vessels. 



The facility with which frequent measurements may be made of the diameter 

 of any selected capillary or minute artery or vein in the web of the frog's foot, is 

 well known to physiologists, and has been taken advantage of by Wharton 

 Jones,* Bennett,! Lister4 and others, in examining their condition during in- 

 flammation. A more general application of such examination of the capillaries 

 to the investigation of the action of poisons would certainly be of great value. It 

 has proved so in the case of nicotia ; § and we cannot consider any research on 

 the actions of a cardiac poison to be complete unless it be done. 



* On the State of the Blood and Blood- Vessels in Inflammation, &c. Guy's Hospital Reports, 



1851. 



f Principles and Practice of Medicine. 



I Philosophical Transactions, 1858. 



§ Claude Bernard, Lecons, &c, 1857, p. 399. 



