514 



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



diastolic pressure. Consequently the sounds produced by finger pressure on 

 the brachial artery, while they somewhat resemble in quality the normal 

 sounds produced by armlet pressure, do not show a perfect similarity to 

 these. Thus, suppose we obliterate the brachial artery with the finger, on 

 releasing it gently we hear for a very short period clear sounds followed by 

 murmurs. These murmurs are not in our experience followed by clear sounds 

 and then by dull sounds, as is the case when the armlet embraces the upper 

 arm. It is obvious that on slightly releasing the occluding pressure the blood 

 flows in jets into the artery, which is relaxed below the seat of compression. 

 Hence the first clear tension sounds. When the artery becomes oval in shape, 

 the clear sounds are dulled by the murmurs. When the artery becomes 

 circular the pulse wave does not suffice to make tense the now patent artery 

 and produce the dull sounds. The finger does not obstruct the peripheral 

 outflow and bring into play the reinforcement due to the vessels of the 

 tissues. 



If we place an armlet distal to the position of the stethoscope, and by the 

 pressure in this armlet obstruct the blood flow, then on compressing the 

 brachial artery with the finger, only clear sounds are heard for a short 

 period as the artery is compressed and released. The murmurs vanish, 

 clear sounds take their place, and the range of sounds is short. As we have 

 pointed out, the whole range of sound is dependent on the resonating effect of 

 the vessels in the tissues surrounding the artery. This resonating effect is 

 absent when an artery is discretely occluded by the finger so that surrounding 

 tissues are not included. 



If an armlet is placed on the upper arm and the external pressure raised 

 till the clear sounds are produced, just below the systolic level, then if the 

 artery be occluded by the finger between the armlet above and the tambour 

 of the stethoscope below, all sounds vanish. Supposing we place the tambour 

 under the lower part of the armlet, then compression of the artery imme- 

 diately distal to the edge of the armlet does not abolish the sounds. They 

 become clearer, because the energy of the pulse spend itself on the mass 

 under the armlet ; the obstruction further tightens up the vibrating drum. 



The sounds are abolished when the finger occludes the artery between the 

 armlet and the tambour ; first, because the artery is not distended by the 

 systolic phase of the pulse wave ; secondly, because the sounds produced under 

 the armlet are not now conducted by the fluid column of blood in the artery. 



Suppose we place the stethoscope under the lower part of the armlet, that 

 is just above the occluding finger, then the sounds are audible just up to the 

 systolic pressure of the blood, e.g., 110 mm. Hg. But if the stethoscope is 

 placed exactly under the upper edge of the armlet, sounds are audible up to, 



