THE SUPRARENAL SYSTEM 235 



of the vagus or by atropine paralysis of the vagal terminals, is 

 almost certain evidence in favour of this theory. It is, however, 

 a more difficult matter to prove that the influence upon the 

 vasomotor centres is secondary, though from what we know of 

 the effects of high blood-pressure upon these centres, the assump- 

 tion seems highly probable. Moreover, the exhibition of adren- 

 alin is followed by other phenomena, due to the stimulation of 

 certain other centres, which are certainly not provoked by the 

 action of the substance itself, but are the result of the increased 

 arterial tension. 



To this group of phenomena belong the changes which are 

 observed in the respiratory conditions after the injection of supra- 

 renal extract or of adrenalin. After the injection of therapeutic 

 doses, the respiration becomes shallow and diminishes in 

 frequency. The shallowness is due to diminution of the 

 inspiratory movements, the reduction in frequency to the pro- 

 longing of expiration. Sometimes there are isolated gasps and 

 sighs, or there may be several prolonged expiratory pauses. If 

 the injections are repeated, the shallowness remains, but the 

 prolonged expirations disappear, and the breathing becomes 

 slightly accelerated (Kahn). At the same time, the height of the 

 expirations remains at the former level. The inspirations 

 gradually become deeper, until, by the time the blood-pressure 

 has fallen to the normal, the depth and frequency of respiration 

 has also reached the normal. 



Boruttau attributed this influence of adrenalin upon expir- 

 ation to a direct inhibitory action, or at least to a reduction in 

 the sensibility to stimuli of the respiratory centre in the medulla 

 oblongata. It would be more accurate, perhaps, to speak of ' ' an 

 increased sensibility to stimulus on the part of the inhibitory 

 centres," especially since Kahn has shown that the respiratory 

 reflexes produced by centripetal stimulation of certain nerves, 

 undergo a marked increase in intensity after the injection of 

 suprarenal extract. Such are, the improved inspiration which 

 follows weak stimulation of the central vagus stump ; the improved 

 expiration which follows stimulation of the superior laryngeal 

 nerve ; and the suspension of expiration (Kratschmer's reflex) 

 which follows stimulation of the nasal branches of the trigeminus. 



We have no proof that these changes in respiratory activity 

 are the result of the direct action of adrenalin upon the respiratory 

 centres; hence we are compelled to regard them, like the changes 

 which take place in the bulbar and vagal vasomotor centres, as 

 the result of changes in the circulatory conditions. 



Among the effects of adrenalin of which we at present know 

 very little, are those influences, perhaps physiological, but more 

 probably toxic, which it exercises upon the striated muscles. 

 According to Oliver and Schafer, suprarenal extract, like veratrin, 

 provokes an extension of the graphic curve of contraction of the 



