AND BLOOD PRESSURE 121 



lation is of the greatest importance in stopping haemorrhage from 

 wounded arteries ; the abolition of contractility produced by 

 freezing explains the extra haemorrhage which results after freezing 

 has been used as a local anaesthetic for minor operations. The 

 contraction of excised arteries, says MacWilliam, is excited by 

 chloroform vapour and adrenalin, and abolished by sodium 

 fluoride. It is a vexed question how far the extreme degrees of con- 

 traction, such as may be excited post mortem, may occur in living 

 arteries in continuity under the influence of drugs, or in disordered 

 states of metabolism. The view has been put forward that such 

 contraction does occur, and that the arteries become so rigid in 

 consequence of it, that serious errors arise in the reading of blood 

 pressure by the accepted methods. It has been asserted that in 

 cases where high readings of blood pressure have been recorded 

 much of the pressure has gone in compressing the stiff walled 

 artery. 



THE ARTERIAL PRESSURE IN MAN 



There are two methods at our choice for measuring the arterial 

 pressure in man. The one, the method of obtaining the maximal 

 oscillation and reading the pressure at which this occurs. The 

 other, the method of finding the pressure at which obliteration of 

 the artery occur and the pulse ceases to be felt. The instrument 

 hitherto ' generally used is the armlet, independently invented 

 by Riva Rocci and by Hill and Barnard, which consists of a 

 rubber bag encased in soft leather. The rubber bag is connected 

 by tubing and T piece to a syringe bulb and a manometer ; the 

 latter may be either a Hg manometer or some form of spring gauge. 



Several forms of sphygmometers have been invented by 

 v. Basch and others for application to the radial artery. Small 

 rubber bags are used and connected with metal spring gauges. 

 The graduation of such spring gauges alters with time, and the 

 writer finds small bags cannot be applied so that the pressure 

 always wholly reaches the artery. Some of it may go to distending 

 the elastic wall of the bag or to distorting the surrounding tissues, 

 and thus large and unavoidable errors arise with the use of these 

 instruments. The rubber bag must be large enough to transmit 

 pressure equally to all parts of the tissues in which the artery lies ; 

 then the tissues protoplasm contains 80 per cent, of water 

 transmit the pressure equally to the artery. The bag must be 



