Phystological Actity of Substances related to Adrenalin. 499 
catechol several milligrammes are required to produce well-marked effects, 
but methylamino-acetylcatechol is more nearly related to adrenalin, and, as 
one would expect, is more active physiologically. The properties of this 
substance have been investigated by Hans Meyer (3) so that it is unnecessary 
to give further details, but it may be noted that about half a milligramme is 
necessary to produce a definite rise in blood-pressure in a rabbit, so that the 
activity of the substance is far inferior to that of adrenalin. 

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Fie. 1.—Rabbit, 2°2 kilogrammes. Carotid B. P. Vagi divided. Urethane. 10 milli- 
grammes catechol. Zero pressure 30 mm. below signal line. Time = seconds, 
If the chlorine in chloracetylcatechol be replaced by hydrogen the product 
acetyleatechol, CgsH3(OH)2.CO.CHs, is still active, but if the hydrogen of the 
hydroxyl groups be replaced, for example, by acetyl groups the product is 
quite inactive. Similarly, although, as previously stated, injection of catechol 
is followed by increase in blood-pressures, the methyl ether of catechol, 
CH3.0.CgH4(OH), produces no such effect and other analogous cases have been 
observed. It may be noted that substitution of the hydrogen of the phenolic 
hydroxyl groups very greatly increases the chemical stability of these 
substances and this, one may well imagine, would tend to result in substances 
of less marked physiological activity. From these results it would appear 
that two free hydroxyl groups in the nucleus are essential constituents of 
active substances in this group and, since of the three isomeric dihydroxy- 
benzenes only catechol produces a rise in blood-pressure after injection, it is 
possible that the hydroxyl groups must be in the ortho position to one 
