128 PEACTICAL PHYSIOLOGY 



higher in the post-tibial than in the brachial by the height of the 

 column of blood which separates the two arteries. The effect of gravity 

 is compensated. The reverse is the effect in states of debility, and the 

 pulse frequency is then greatly accelerated in the vertical posture. 

 The venous pressure may be obtained by placing the armlet round the 

 fore-arm, raising the pressure in it, emptying the blood out of a vein 



FIG. 128. Spring sphygmometer. The leather armlet encloses a rubber bag. The 

 bicycle pump is used to raise the pressure. The spring manometer indicates the 

 maximal pulsation and the pressure. 



above the armlet by digital pressure, and then diminishing the pressure 

 until the vein suddenly fills. Note the pressure when this happens. 



Place the other armlet round the upper arm and raise the pressure in 

 it nearly to the systolic pressure, keep it at that, and observe that 

 the venous pressure rises after a minute or so to this pressure. Observe 

 the effect on the veins of holding the arm in the dependent posture 

 and motionless, of contracting the muscles, of raising the arm, etc. 



CHAPTER XXXIII. 



BLOOD. THE HAEMOGLOBINOMETER AND THE 

 HAEMACYTOMETER. 



Gowers-Haldane Haemoglobinometer. The maximal error of this 

 admirable instrument is not more than 0'8 per cent. The standard 

 solution in tube D is a 1 per cent, solution of ox blood saturated with 

 coal gas. 1 The oxygen capacity of the ox blood from which the 

 standard was prepared was 18*5 per cent. This was determined by 



1 Coal gas contains carbon monoxide as an impurity. 



