384 



SCIENCE 



[N. S. Vol. XLV. No. 1164 



sisippi during the last four years, has been 

 promoted to be professor of municipal engi- 

 neering. 



Me. D. Keilin, of Magdalene College, Cam- 

 bridge, has been appointed assistant to the 

 Quick professor of biology. 



DISCUSSION AND CORRESPONDENCE 



THE ROLE OF BOYLE'S LAW IN CLINICAL 



SPHYGMOMANOMETRY. A REPLY 



TO A. M. BLEILE 



In a paper read before the American Physio- 

 logical Society Dr. Bleile^ discusses an appli- 

 cation of Boyle's law which I made in devel- 

 oping the theory of the oscillations of pres- 

 sure produced in the compression chamber of 

 a sphygmomanometer by the arterial pulse.^ 

 My statement of this law, worded so as to fit 

 the conditions obtaining in my experiments, 

 was as follows : "... the rise of pressure 

 determined by the addition of a given volume 

 of incompressible material to a confined, gas- 

 filled space is proportional to the pressure of 

 the gas filling the space." Dr. Bleile illus- 

 trates the action of the law by paraphrasing 

 the example in my paper thus : 



With a given volume pulse change, if the arm 

 band pressure is at 100 mm., the pulse wave shown 

 by the arm band manometer would be only half as 

 great as it would with the same volume pulse but 

 with the arm band pressure at 200 mm. 



He then goes on to say that 

 upon testing this hypothesis by the help of a suit- 

 able physical model it is demonstrated that such is 

 not the case. On the contrary, it is demonstrated 

 that the oscillations of volume occupied by a given 

 mass of gas produce inversely proportional oscil- 

 lations of absolute pressure. Or, in other words, 

 the absolute pressure of a given mass of gas is 

 inversely proportional to the volume. . . . There- 

 fore, the results of the present work are in har- 

 mony with Boyle's law but are contrary to Er- 

 langer's hypothesis. 



This statement would lead one to suppose 

 i"Au Application of Boyle's and Avogadro's 

 Law to the Oscillations of the Manometer in Clin- 

 ical Measurements of Blood Pressure, ' ' Am. Jour, 

 of Physiol., 1917, XLII., 603. 



2 ' ' The Mechanism of the Oscillatory Criteria, ' ' 

 Am. Jour, of Physiol, 1916, XXXIX., 401. 



that in my application of Boyle's law I have 

 committed the mistake of making the relation 

 between pressure and volume a direct instead 

 of an inverse one. This, however, is not the 

 case. If my statement of the law is compared 

 with Dr. Bleile's, it vnll be found that in this 

 respect there is not the slightest difierence 

 between them. Thus, to paraphrase my state- 

 ment so as to make it conform with Dr. 

 Bleile's, " the addition of a given volume of 

 incompressible material " reduces the volume 

 of the given mass of gas ; this reduction causes 

 a " rise of pressure," which " is proportional 

 to the (initial) pressure of the gas filling the 

 space." In this statement the relation be- 

 tween volume and pressure (italicized) obvi- 

 ously is an inverse one. What evidently con- 

 fused Dr. Bleile is the introduction into my 

 statement of the word " proportional " for the 

 purpose of expressing the relation between the 

 initial pressure of the confined gas and the 

 final pressure developed upon reducing its 

 volume. That this relation is correctly ex- 

 pressed can easily be, and has been, confirmed 

 by the use of very simple apparatus. 



Having made it clear that there is no dis- 

 crepancy between my and Dr. Bleile's state- 

 ments of Boyle's law, I now desire to add that 

 Dr. Bleile is right in criticizing my example 

 of the application of the law. For I inadvert- 

 ently employed in the example the pressures 

 read directly from the mercury manometer 

 instead of the absolute pressures, though, in 

 the form in which Dr. Bleile repeats it, the ex- 

 ample is in perfect accord with Boyle's law, 

 if it is understood that the pressures are abso- 

 lute. The failure to express the pressure in 

 absolute terms affects, however, only the mag- 

 nitude of change, not its sign, and therefore 

 does not alter in any material way the devel- 

 opment of the theory of the compression oscil- 

 lations; for my only object in invoking Boyle's 

 law was to show that under the particular set 

 of ideal conditions premised, namely a rigid 

 compression chamber, a compressible trans- 

 mitting medium and an inextensible artery, 

 the amplitude of the pressure oscillations re- 

 sulting from the filling and emptying of the 

 artery must increase as the compressing pres- 



