1895.] it* Natural History, Chemistry, and Pharmacology. 73 



and by Gley in 1888, by Sailer in 1891, by Paschkis in 1892, and by 

 Lewin in 1893, has been more fully described. 



The group of arrow-poisons which owes its activity to extracts of 

 Acokanthera plants has been found to possess a qualitative identity of 

 action with Strophanthus, but some of the authors mentioned 

 emphasise an action upon the cardio-respiratory centres in the 

 medulla, and others a direct action upon the heart. 



A detailed examination of the pharmacological action of acokan- 

 therin has not led to the discovery of any important qualitative 

 differences between its action and that of Strophanthus hispidus and of 

 its active principle strophanthin, which was described by one of us in 

 1870, in 1872, and in 1890. 



As, however a special interest must be attached to the effects upon 

 the circulation, the experiments upon the heart, blood-vessels, and 

 blood-pressure are described with more detail than those upon other 

 systems. Our experiments show that small and carefully-regulated 

 doses can produce a great slowing of the rate of the heart, even when 

 the vagi nerves are divided, or when atropine is administered ; and 

 that a great increase in the extent of the diastolic and systolic move- 

 ments of the heart can be obtained without the average blood- 

 pressure being at all affected, or affected only to a very small extent. 

 Any rise of blood-pressure which follows the administration of such 

 doses is accompanied by so great a slowing of the rate and by so great 

 an increase of the extent of the pulse movement that constriction of 

 blood-vessels seems contra-indicated ; and the rise of blood-pressure 

 must therefore be attributed to the increase in the amplitude and 

 vigour of the heart movements and the greater quantity of blood 

 propelled into the arteries. Large doses produce a rise of blood- 

 pressure, which is probably due to an action upon the vaso-motor 

 centres or peripheral ganglia, and probably not upon the muscle of 

 the blood-vessels, because perfusion experiments in frogs show that 

 dilute solutions of acokantherin of 1 in 100,000 to 1 in 10,000 in 

 normal saline do riot produce contraction of blood-vessels, and with 

 even so strong a solution of acokantherin as 1 in 5000 the contraction 

 is very slight ; whereas a solution of digitalin of 1 in 100,000 to 1 in 

 20,000 in normal saline rapidly reduces and arrests the flow through 

 the blood-vessels. 



The predominant action of acokantherin is that exerted upon 

 striped muscle, and, because of this action, with possibly an action 

 upon the intrinsic cardio-motor ganglia, the chief effect is produced 

 upon the heart, while the influence exerted upon the cardio-respira- 

 tory centres in the medulla is relatively slight or secondary. 



