522 Messrs. M. Flack, L. Hill, and J. McQueen. 



In one such experiment the following were recorded : — 



O om pre s s ion . 



JJeiormation. 



CJutnow per minute. 



L/I16 lerjgtn oi artery — 





c.c. 



H«0 



\j in, uav/ 



Nil 



210 



15 



Nil 





45 



Begins to flatten visibly in diastole 



160 



85 



Flat in systole 



Nil 



Two lengths of artery — 







em. H 2 



Nil 



182 



15 „ 



Second length of artery begins to deform 



186 



45 „ 



Second length flat in diastole 



106 



67 „ 



First length of artery flat in diastole 



Drops 



85 



First length of artery flat in systole 



Nil 



In Experiment I the conditions, of course, are not the same as those which 

 pertain in the arm, for in the arm there is the capillary field with its resist- 

 ance which precludes the pulse from reaching the veins. However, the 

 experiment shows that the behaviour of the artery is notably influenced by 

 the compression of a vessel placed distally to it, and therefore that the study 

 of the compression of a length of artery placed in a simple schema does not 

 suffice to elucidate the compression of the brachial artery in the arm. 



This conclusion is confirmed by Experiment II. 



Experiment II. 



We repeated Experiment I, but recorded the pressure in the tube which 

 joined the first and second length of artery. On raising the compression to 

 5 cm. H 2 the second length of artery began to flatten in diastole, the first 

 length became distended in diastole, and the record then showed a rise in 

 pressure. A maximal pulse developed as the compression increased. 



Off. On. Off. On. 



Fig. 6. 



