THE PHARMACOLOGICAL ACTION OF HARMINE. OE 
some reduction in the amplitude of its excursus due to less complete systolic contraction. 
Solutions of 1 in 50,000, or weaker solutions, have no eftect on the heart. 
A point of some interest, when taken into consideration with the effect of harmine 
on blood pressure in mammals, is the extreme readiness with which the heart recovers 
when the harmine is removed from the circulation. 
Other experiments have shown that the slowing of the heart produced by harmine 
is not prevented by simultaneous perfusion with atropine sulphate, and is therefore due 
to an action on the cardiac muscle. 
(b) Blood-vessels. 
To ascertain any changes produced by harmine on the blood-vessels of the frog, the 
following method was used. After the frog was pithed and the heart exposed, the 
venz cave were cut across, and a fine cannula was tied into the left aorta, the right 
aorta being ligatured. ‘his cannula was connected with two Marriotte’s flasks containing 
the fluids to be perfused. A record was taken of the amount of fluid exuding per minute 
from the cut venze cavee. Ringer's solution was used as the normal solution and as the 
solvent for harmine. 
Perfusion of the vessels for thirty minutes with solutions of harmine of varying 
strengths gave the following results:—A solution of 1 in 1000 reduced the flow from 
1°8 ¢.c. per minute to 0°9 ¢.c. per minute; a solution of 1 in 2500 reduced the flow 
from 2°4 ¢.c. per minute to 1°7 ¢.c. per minute; a solution of 1 in 5000 reduced the 
flow from 2°7 c.c. per minute to 2°0 c.c. per minute; while a solution of 1 in 7500 had 
no effect on the flow through the vessels. Harmine has therefore a slight constricting 
action on the frog’s blood-vessels. 
(c) Heart and Blood-vessels. (Blood Pressure.) 
In all blood-pressure experiments the animals (rabbits or cats) were first anzesthet- 
ised with chloroform ; the trachea was then exposed, and a cannula tied into it through 
which diluted ether was thereafter inhaled. A cannula in the left carotid artery was 
connected with the manometer. Respirations were recorded by means of a double 
stethograph attached by a band round the thorax and connected with a Marey’s 
tambour. Injections were made into the right jugular vein. It was found in pre- 
liminary experiments that the minimum lethal dose of harmine injected in this way IS. 
about 0°03 gramme per kilo. 
Experiment 24 (Table VIL., figs. 9 Pan 10).—Rabbit, 2400 grammes. The first. 
injection of 0°01 grm. per lal, equivalent to one-third of the intravenous minimum 
lethal dose, produced a somewhat transient fall of blood pressure, the normal level 
being restored in about ten minutes. The fall of pressure was accompanied by a 
slowing of the heart, which was evidently, in part at least, a causal factor. Recovery 
of blood pressure occurred in spite of further slowing of the heart. It is noteworthy 
TRANS. ROY. SOC. EDIN., VOL. XLVIIL, PART I. (NO. 4). 14 
