342 THE DUCTLESS GLANDS [CH. XXV. 



longation of the period of relaxation. The effect on involuntary 

 muscle is even more marked ; there is an enormous rise of arterial blood- 

 pressure due chiefly to a contraction of the arterioles. This is produced 

 by the direct action of the extract on the arterioles, not an indirect 

 one through the vaso-motor centre.* The substance in the extract that 

 produces the effect is known as adrenaline; it is confined to the 

 medulla of the capsules, and is absent in cases of Addison's disease. 



The suprarenal bodies, therefore, form something which is dis- 

 tributed to the muscles and is essential for their normal tone ; when 

 they are removed or diseased, the effects seen are the result of the 

 absence of this internal secretion. 



Adrenaline has received various names from the different chemists 

 (Abel, v. Fiirth, Takamine, etc.), who have isolated it. It is very 

 powerful ; solutions of one part in a million will produce physio- 

 logical effects. Its composition is shown by the following formula : 



OH 



/\ OH 



CH.OH.CH,.NH.CH.j 



and it is therefore a methyl-amino derivative of catechol (Pauly, 

 Jowett). Eecently, compounds closely allied to it in composition 

 and action have been made synthetically (Stolz, Friedmann, Dakin). 



Whether this discovery will lead to the same kind of results, as 

 in the case of the thyroid, must be left to the future to decide. 

 There is already some evidence to show that injection of suprarenal 

 extract is beneficial in cases of Addison's disease. The discovery of 

 adrenaline itself is, however, one of immense practical importance. 

 Its action on the small blood-vessels is so powerful that quite weak 

 solutions applied locally will subdue the congestion of inflammation 

 and even arrest haemorrhage. 



The splanchnic nerves have been shown to contain secretory fibres 

 which control the amount of adrenaline poured into the circulation. 



The use of the suprarenal cortex is still unknown. It has been 

 suggested that it has some effect on the development of the organs of 

 generation, but these views are quite hypothetical. The cortex, how- 

 ever, contains large quantities of lipoid material (cholesterin, lecithin, 

 and similar substances), and the droplets seen in the fresh cells consist 

 of these compounds ; the suggestion that the suprarenal cortex plays 

 a part in the metabolism of these substances appears to be the only 

 feasible one at present. 



* It is the sympathetic nerve terminals which are really affected. Any muscular 

 tissue supplied by sympathetic nerves contracts under the influence of adrenaline. 

 Vessels destitute of constrictor fibres (coronary, pulmonary and cerebral) are not 

 contracted by adrenaline. 



