THE SUPRARENAL SYSTEM 187 



usually introduced into the tissues by subcutaneous injection ; 

 where, however, the mucosa are acutely inflamed and hyperasmic, 

 the local application, either by instillation or by painting the sur- 

 face, has a similar effect. 



J. Baum has pointed out that the effect of suprarenal sub- 

 stance in producing blanching of the skin will be the more 

 energetic, prompt, and sustained, the more nearly the condition 

 of the vessels approximates to the normal. In acute inflammatory 

 conditions the action is marked ; where, however, the condition of 

 the vessels is chronically pathological, as well as in all forms of 

 destructive disease, the anasmia produced by adrenalin is slight 

 and very transient, and telangiectatic veins do not become 

 emptied. As soon as the anaemia passes, normal tissue regains 

 its normal appearance, and hyperaemia supervenes only after 

 repeated employment of the drug; but where there are chronic 

 pathological changes in the tissue, the first application is followed 

 by pronounced venous hyperaemia. 



Upon which part of the vessels does adrenalin act ? There 

 is no doubt that, in large and small arteries with muscular walls, 

 adrenalin produces a contraction of the musculature. It is a 

 remarkable fact that, where adrenalin is employed locally, those 

 injections disappear first which are described as parenchymatous, 

 and it is more than probable that this is due to an enlargement 

 of the capillaries. Further, it has been observed that, where 

 adrenalin is applied locally to reduce parenchymatous haemor- 

 rhage, not only do the great vessels not contract, but, owing 

 obviously to the increased peripheral resistance, the great arteries 

 have a stronger beat. If the circulation of frogs is watched 

 through the microscope it will be seen that, after the introduction 

 of adrenalin, the circulation in the capillaries is suspended at a 

 moment when the blood in the arteries supplying them is still 

 flowing with undiminished rapidity (Bukofzer). When adrenalin 

 is injected into the veins, the volume of the organ decreases and 

 the parenchyma becomes pale, but the great arteries which supply 

 the organ are rather dilated than otherwise, and their beat is 

 stronger ; this is well seen in the mesentery, after the exposure of 

 a loop of the intestine. 



Since the contractility of the capillaries and their motor inner- 

 vation was proved by Steinach and Kahn, the part played by this 

 portion of the vascular system in the vaso-contraction produced 

 by adrenalin, can no longer be doubted. These authors showed 

 that there is a similarity of process between the contraction of 

 an artery and the contraction of a capillary ; for, in response to 

 certain stimuli, the branched cells in the capillary wall (discovered 

 by Rouget and S. Mayer) contract, and may so reduce the vessel 

 as to entirely obliterate the lumen. An object eminently suited 

 to observation of capillary conditions is the nictitating membrane 

 of the living frog ; if this is watched under the microscope, it 



