304 



Messrs. J. G. Bramwell and A. V. Hill. 



writing lever. The two levers, lying close together, write upon the same 

 revolving drum, and indicate the moments of arrival of a wave in the mercury, 

 at X and at Y respectively. The wave is set up by hitting or squeezing the 

 left-hand rubber pipe at some distant spot. Its arrival at X causes a sharp 

 movement of the writing-point at X, it is then transmitted with very high 

 velocity through the almost rigid copper pipes, being delayed, however, in its 

 arrival at Y by the slow transmission across the elastic artery between 

 A and B. 



After the experiment on the artery is completed, the artery is replaced by 

 a rigid copper pipe from A to B, and the observations are repeated, the small 

 time interval observed when the rigid tube lies on the path of the wave being- 

 subtracted from the larger interval when the elastic tube is there. In 

 this way any small " zero error " in the instrument is practically eliminated. 

 Corresponding points on the records of the two writing levers are com- 

 pared, and the time interval between theui can be determined with reasonable 

 accuracy. Greater accuracy could doubtless be secured by employing a 

 photographic method of recording the arrival of the wave at X and Y, but 

 for the present purpose this was not necessary. 



The artery employed was the common carotid of a young man (who had 

 died of malignant endocarditis). It measured 6 - 84 cm. between the ends of 

 the copper pipes. At each pressure a series of observations was made of the 

 interval between the arrival of the wave at X and Y (fig. 1), and the 

 " probable error " of the mean values given below, lay between 0-0005 

 and 0-001 sees. The " zero error " to be subtracted, as estimated by the 

 interval observed when the artery was replaced by a copper pipe, was 

 as follows : — 



Pressure (mm.) 



20 



40 



60 



80 



100 



Zero error (6ecs.) 



-0135 



-0142 



0150 



-0157 



0165 



Pressure (mm.) 



120 



140 



160 



180 



200 



Zero error (sees.) 



-0174 



-0182 



'0190 



-0198 



-0206 



The following Table shows the results of a series of observations on the 

 artery. The values for blood are obtained by multiplying by 3"58. 



Pressure (mm.) 



Interval observed (sees.) 



Zero error (sees.) 



Difference (sees.) 



Velocity (metres p.s.) . . . 

 Velocity, blood (m.p.s.) 



25 



57 



78 



92 



110 



152 



200 



0-079 



0-086 



-0665 



0-052 



0-0465 



-0380 



-0338 



0-014 



0-015 



-0156 



0-016 



-0170 



0-0187 



-0206 



-065 



0-071 



-0509 



0-036 



-0295 



-0193 



-0132 



1 -05 



0-96 



1-34 



1 -90 



2 32 



3 -55 



5-18 



3 76 



3-45 



4 -81 



6 -80 



8 3 



12 7 



18 5 



