86 



PEACTICAL PHYSIOLOGY 



The venous pressure may be obtained by pressing the instrument on 

 to a vein on the back of the hand, emptying the blood out of the 

 vein by digital pressure, and then diminishing the pressure until the 

 vein suddenly fills. Note the pressure when this happens. 



CHAPTER XX. 



BLOOD. THE HAEMOGLOBINOMETER AND THE 

 HAEMACYTOMETER. 



Gowers-Haldane Haemoglobinometer. The maximal error of this 

 admirable instrument is not more than - 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 

 displacing the oxygen from laked ox blood with ferri-cyanide 



FIG. 87. Gower's haemoglobinometer. 



of potassium, and measuring the amount of gas. The per- 

 centage of haemoglobin corresponding to 18-5 per cent, is about 

 13-8 per cent. The normal human blood when saturated with CO and 

 diluted with water to the mark 100 in tube C corresponds in tint 

 to the standard, and has therefore an oxygen capacity of 18-5 per cent. 

 Add distilled water to tube C up to the mark 20. Take exactly 20 

 c.mm. of blood in the pipette, and blow it into C. Pass a narrow glass 

 tube connected with a gas burner into the free part of tube C. Turn 

 the gas on and push the glass tube down near to the blood. The gas 



1 Coal gas contains carbon monoxide as an impurity. 



