230 



INTERNAL SECRETION 



systems. In the case of the latter systems, the relationship 

 between nerve and muscle is biochemical and similar to that 

 between nerve and muscle in striated muscles. 



The sensibility of a muscular tissue to adrenalin is propor- 

 tional to the degree in which the myoneural junction is differenti- 

 ated, and this, in its turn, seems to depend upon the frequency 

 of the impulses which, under normal conditions, it receives 

 through the agency of the sympathetic. In other respects, its 

 irritability is independent of the nervous impulses. 



Owing to the fact that its trophic centre is situated, not in the 

 nerve cell but in the muscular nucleoplasm, the irritability of the 

 myoneural junction is not destroyed "by degenerative resection of 

 the nerve. On the contrary, we sometimes encounter the startling 

 phenomenon of a denerved and decentralized tissue having a 

 hypersensibility to chemical stimulation by adrenalin. The 

 " paradoxical dilation of the pupil " which, after denervation 

 (extirpation of the superior cervical ganglion), follows the instil- 

 lation of adrenalin into the eye of rabbits and of cats, while the 

 normal eye of these animals does not react to adrenalin, has 

 already been described. As we then pointed out, this phenomenon 

 is explained by the suppression of the inhibitory sympathetic 

 fibres. Elliott believes, however, that it is rather due to increased 

 irritability of the denerved peripheral tissue. 



After denervation, the blood-vessels, the retractor muscle of 

 the penis, and the hair muscles all react to adrenalin. That, after 

 denervation, adrenalin also increases inhibitory activity, such, for 

 instance, as that of the urinary bladder, is highly probable, but 

 as yet without definite proof. 



This hypothesis explains a number of peculiarities in con- 

 nection with the action of adrenalin, some of which have long 

 been recognized. It is well known that, in cats, while adrenalin 

 is active, stimulation of the vagi does not produce cardiac 

 inhibition, stimulation of the depressors is not followed by a fall 

 in blood-pressure, nor stimulation of the nervi erigentes by con- 

 traction of the urinary bladder. As soon as the effect of adrenalin 

 has passed off, the muscles respond to stimulus in the usual 

 manner. There was a general disposition to ascribe to adrenalin 

 a transitory paralysing action upon the terminals of the cranial 

 and sacral autonomous nerves. We now know that adrenalin 

 effects an almost maximal stimulation of the myoneural 

 sympathetic terminals, and that it produces results which are 

 dependent upon these. It is obvious, therefore, that, in each 

 organ, the response to electric stimulus can be changed by the 

 action of adrenalin only in a manner and to a degree such as 

 would result from a strong stimulation of the sympathetic nerve- 

 fibres. While adrenalin is active, stimulation of the sympathetic 

 does not produce more intense activity. When the adrenalin 

 action has passed off, the results of such stimulation are neither 



