58 THE APPLIED PHYSIOLOGY 



pressure induced gradually falls. The Riva-Rocci 

 sphygmometer is to be read, by the level of a column 

 of mercury, at the point where the pulse, at first 

 obliterated by the pressure, becomes just percept- 

 ible to the finger or the ear. This gives the systolic 

 pressure. The diastolic is read by noting the point 

 of maximum oscillation of the column of mercury. 

 The apparatus of Hill and Barnard is to be read on 

 a pressure gauge when the recording needle shows 

 the greatest oscillation ; this gives the diastolic 

 pressure. An average reading for the maximum or 

 systolic pressure is no to 120 millimetres of mercury ; 

 for the diastolic pressure a little less. The figure is 

 seldom continuously below 100 (except in Addison's 

 disease), but it may be higher than 200 in arterio- 

 sclerosis. 



For the study of cases of raised or lowered 

 blood-pressure these instruments are essential, 

 and are very widely used to-day. We shall, how- 

 ever, consider them rather in their surgical appli- 

 cation. 



Methods for the measurement of venous and 

 capillary pressure have been introduced more 

 recently, and are of less clinical value so far. Venous 

 pressure may be determined by stroking a vein until 

 it becomes empty up to a valve, then applying 

 the Riva-Rocci sphygmometer, and noting the 

 pressure at which the vein fills. Capillary pressure 

 may be obtained by determining to what height 

 above the arm normal saline in a funnel must be 

 raised before it will begin to flow through a hypo- 

 dermic needle into the subcutaneous tissues (Leonard 



