60 



The Endocrine Organs 



dilated by the extract. (According to Barbour, the human coronary arteries 

 are constricted, whilst those of the calf, sheep, pig, and other mammals are 

 dilated (inhibited).) It is always the smaller vessels which are most 

 affected, and in consequence of the great rise of pressure which their con- 

 traction produces the larger arteries tend to become passively dilated : this 

 dilatation may be very great. The effect upon the vessels is seen after com- 

 plete destruction of the central nervous system, and after severance of the 

 nerves to the part (fig. 38) : still more after the nerves to the vessels have 

 been severed for a loner time. It is therefore due to a direct action of the 



Fig. 36. — The same as fig. 35, but with vagi cut. 



autacoid principle of the gland upon the contractile tissue. Nevertheless, 

 in the case of suprarenal extract such action only occurs in tissues which 

 are supplied with nerves from the sympathetic system, and in the embryo 

 in these tissues only after they have received their nerve-supply (M'Fie). 

 And, as has just been stated, severance of the nerves, so far from stopping 

 the action, tends on the contrary to make the tissues supplied by the 

 severed nerve more easily excited by the autacoid. This has been found to 

 apply not only to the blood-vessels, but also to the pupil (Meltzer and Auer) 

 and to the retractor penis (Fletcher), and is probably of general application. 

 Gunn and Chavasse have further shown that adrenalin acts upon the 

 muscular coat of veins, causing tonic contraction of the peripheral veins and 

 increased rhythmic contraction of the superior vena cava near the heart. 



If the vagi are paralysed by atropine, as small a dose of adrenalin as -0003 milli- 

 gramme per kilo body-weight injected into a rabbit's vein will cause a distinct rise of 



