130 PHYSIOLOGY FOR DENTAL STUDENTS. 



The most striking proof of their importance is obtained by in- 

 jecting an extract of the medulla of the adrenal gland into a 

 vein. It causes an immediate rise in blood pressure, which is 

 more or less proportional to the strength of the extract. The 

 rise is accompanied by a slowing of the heart, due to the reflex 

 stimulation of the vagus centre excited by the rising blood pres- 

 sure. When this reflex slowing is rendered impossible by cutting 

 the vagi, the rise in blood pressure following the injection may 

 be enormous. The active substance in the extract is called adren- 

 alin, suprarenin, adrenin or epinephrin. It is a comparatively 

 simple chemical body, having the formula: 



(HO)C 



CH 

 /\ 



CHCH (OH) CH 2 NHCH a 



CH 



\/ 



CH 



and existing in two varieties which differ from one another ac- 

 cording to the direction to which the plane of polarized light is 

 rotated. The variety rotating to the left is, by many times, 

 stronger in its physiological actions than that which rotates to 

 the right. The discovery of its chemical structure has made it 

 possible for chemists to prepare suprarenin synthetically, and 

 also to prepare a series of related substances having less marked 

 properties of a similar kind. These are closely related to certain 

 of the bodies which appear during the putrefaction of meat. 



By careful studies of the action of the suprarenin, or related 

 substances, it has been found that the rise in blood pressure, above 

 referred to, is due to stimulation of the muscle fibers in the walls 

 of the blood vessels. It is on this account that a weak solution of 

 suprarenin is used to stop haemorrhage, as after removing polypi 

 from the nose, or in bleeding from the gums, as after tooth ex- 

 traction. The muscle of arteries is by no means the only struc- 

 ture on which adrenalin acts ; indeed it stimulates every structure 

 which is capable of being stimulated by the sympathetic nervous 

 system (see p. 277). Thus, it causes the pupil to dilate, saliva 



