534 



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



A. The first effect of compressing schema I was to increase the amplitude 

 of the pulse in schema II (fig. 20). In this experiment the pulse in 

 schema II was largest when the compression in schema I rose to 40 cm. H2O. 



On compressing the arm the pulse in the radial at first increases in 

 amplitude — a fact well known to clinicians. The tracing in the previous 

 paper shows this increase in amplitude as recorded in the radial artery. 

 Our explanation of this phenomenon is as follows : — 



The first effect of increasing the compression was flattening of the venous 

 outlet which lay in the first schema. The resistance to outflow was thus 

 increased and, in consequence, the diastolic pressure rose and the arteries 

 and tissue schemata became more rigid, i.e. less labile. Therefore the pulse 

 was less spent on the lability of the artery in the first schema and reached 

 the second schema with greater force. On decompression of the first schema 

 the pulse reappeared in the second schema at a lower degree of pressure 

 than that at which it disappeared on compression of the first schema. 



This was only the case, let it be noted, when the decompression was rapid 

 (fig. 21). As we have said before, the same phenomena is often observed 



Off. On. 

 Tig. 21. 



when the systolic pressure is measured on man. The reappearance of the 

 pulse generally gives a lower reading than the disappearance. On rapid 

 decompression the tissue schema I was suddenly made easily extensile and, 

 in consequence, the diastolic pressure of the artery fell and its lability 

 increased. So, too, in the case of the arm when the pressure of the armlet is 

 reduced. The full force of the pulse will not reach the second schema (or 

 forearm) until the first schema (or upper arm) is filled and the artery 

 rendered tenser. If the forearm is previously emptied of blood by elevation 

 and bandaging before compression, it takes much longer for the pulse to 

 return to its full force on decompression — the bandage being removed before 

 decompression is made. This, too, was the case when the second schema was 

 compressed before the first schema was compressed, and the compression of 

 the second schema removed just before the decompression of the first schema. 



