272 THE PHARMACOLOGICAL ACTION OF HARMALINE. 



In the frog, after destruction of the central nervous system, harmaline constricts 

 the blood-vessels when perfused through them. 



In mammals, small doses of harmaline cause a rise of blood pressure — always in the 

 rabbit, and sometimes in the cat. The rise is due to contraction of the arterioles, and 

 is accompanied by a diminution in the rate of the heart. Large doses produce a fall 

 of blood pressure due to slowing and weakening of the heart. 



The slowing of the heart produced by an initial small dose is partly due to reflex 

 stimulation of the vagus by the rise of blood pressure ; that produced by larger doses 

 is independent of vagus stimulation, and due to an action on cardiac muscle. 



In frogs, paralysis of respiration is an early effect of lethal doses ; and in mammals, 

 arrest of respiration, due to paralysis of the respiratory centre, is the chief cause of 

 death from harmaline poisoning. In the latter there is frequently an initial stage of 

 increased respiratory activity. 



Large doses of harmaline cause a fall of temperature in mammals ; the fall is 

 slight with non -lethal doses, but may be profound in the case of a slowly lethal dose. 



Harmaline exerts a powerful action on uterine muscle in the direction of inducing 

 sustained tetanic contraction. 



Harmaline can therefore no longer be regarded merely as a respiratory and 

 convulsant poison. It differs from most alkaloids in that it does not exert, to the 

 same extent as they do, a selective action on one kind of tissue. It attacks not only 

 highly specialised tissues such as voluntary muscle, muscle of the heart, blood-vessels, 

 and uterus, and cells of the central nervous system, but also less highly differentiated 

 cells, such as pigment cells, protozoa (Raab), and ciliated epithelium (Jacobson). 



In this account of its pharmacology the actions of harmaline have been shown to 

 resemble very closely those of another alkaloid, of which the above type non-selective 

 action is also true, viz. quinine. As a pharmacological agent, harmaline ought to be 

 grouped with quinine, and therefore with those substances which are conveniently, if 

 somewhat indefinitely, termed " protoplasmic poisons." 



Considering the close resemblance in the pharmacological actions of harmaline and 

 quinine, one is led to anticipate some corresponding similarity in their therapeutic 

 effects. With this subject I hope to deal on a future occasion. 



