592 VETERINARY PHYSIOLOGY 



dilatation of the coronary arteries. Hoskins finds that in very 

 small doses it causes dilatation of all the arterioles. That it 

 does not act directly on the muscle fibres is shown by the fact 

 that, after the administration of apocodeine which poisons the 

 endings of the abdomi no-thoracic or true sympathetics, it no 

 longer acts, although barium salts still cause a contraction, 

 because theyact directly on the muscle (p. 455). Ergotoxin poisons 

 the endings of the augmentor fibres of the true sympathetic, 

 and, after it has been administered, adrenalin may cause a 

 dilatation of vessels because its action on the endings of the 

 inhibitory fibres is thus unmasked. 



In fact, the action of adrenalin is absolutely specific, and 

 consists in a stimulation of the endings of the true sympathetic 

 nerves. It thus produces on any organ the effect which is 

 produced by stimulating these nerves. 



(2) On the Heart. If the vagi are intact, it produces a 

 slowing which is due to the raised arterial pressure (p. 420). 

 When the vagi are cut it causes an acceleration and generally 

 an increased amplitude of contraction by stimulating of the 

 augmentor endings. 



(3) On the Alimentary Canal it acts, as does stimulation of 

 the splanchnic nerves, by inhibiting peristalsis and stimulating 

 the sphincters (p. 333). ^ 



(4) On the Bladder its action varies in different animals 

 according to whether motor or inhibitory fibres pass to the 

 organs through the splanchnics by way of the inferior 

 mesenteric ganglion and hypogastric nerves (p. 582). In the 

 former case it causes contraction (ferret) ; in the latter case 

 relaxation (cat). 



(5) On the Uterus it generally causes contraction, but, in 

 the virgin uterus, it may cause relaxation, showing that its 

 action may be modified by the functional condition of the 

 tissue. 



(6) On the Iris, when applied to the excised eye of the 

 froo", it has the same action as stimulation of the cervical 

 sympathetic — it dilates the pupil. But in mammals this occurs 

 only when (a) the superior cervical ganglion has been excised — a 

 procedure which is suj^posed to make the nerve terminations 

 more sensitive ; and (h) in some cases of de-pancreatic diabetes 

 (p. 357). Hence it has been concluded that an internal secretion 



