THE SUPRARENAL SYSTEM 2OJ 



sympathetic innervation. Scott Macfie found that the cardiac 

 movements of an embryo chick, two to three days old, were 

 entirely unaffected by adrenalin. According to Kuliabko, the heart 

 of the human embryo is very little influenced by this substance. 

 Quite recently, I found that the heart of the embryo chick is 

 insensitive to adrenalin at a time when the vessels of the vascular 

 area contract readily in response to this substance. Upon the 

 fifth to seventh day, when the intrusion of sympathetic elements 

 has already taken place and a substance which, upon the ground 

 of its biological reactions, is assumed to be adrenalin, is present in 

 embryonic extract, the response of the heart to adrenalin stimulus 

 is clearly shown in the acceleration of the contractions and in 

 single arhythmic beats. 



Dixon's experiments with apocodein supply definitive in- 

 formation concerning the actual site which adrenalin affects in 

 the mammalian heart. 



The immediate effect of apocodein is to produce a paralysis 

 of the inhibitory vagal nerve endings in the heart. At this stage, 

 adrenalin acts in the same manner as upon a heart in which the 

 vagal terminals have been paralysed by means of atropine ; that 

 is to say, it brings about an increase in the rate and the volume 

 of the beats. Further doses of apocodein have the effect of entirely 

 neutralizing the action of adrenalin. The increase in the pulse- 

 rate (from 93 to 211 a minute) produced by adrenalin almost en- 

 tirely disappears (93 to 101), and a still further application of 

 apocodein is followed by an actual fall (87). Even when used 

 in large doses, adrenalin fails to either accelerate or strengthen 

 the systole. The effect of apocodein is to paralyse the acceleratory 

 nerve endings, upon which adrenalin exercises a stimulating 

 influence. 



These results seem to show that the action of adrenalin 

 consists in a stimulation of that portion of the sympathetic 

 apparatus whose function it is to promote cardiac activity. 



This assumption is confirmed by certain phenomena, recently 

 observed after intravenous adrenalin injection by means of the 

 electrocardiograph, by R. H. Kahn, some of which phenomena 

 are also obtainable by means of strong artificial stimulation of 

 the vagus nerve. Such are the prolonging of the refractory 

 period, the heart-block, and the automatic and weakened 

 ventricular beat. The phenomenon which is specific to adrenalin 

 is the disassociation of the auricular and ventricular beats, which 

 is continued for some time, and in the course of which the 

 ventricular beat gives normal electrograms. After resection of 

 both vagi, all these phenomena disappear, and the rise in blood- 

 pressure is recorded without important changes in the electro- 

 cardiogram. 



The Digestive Tract. Strips cut from the oesophagus or 

 stomach of frogs, when fresh, possess considerable tone, but 



