ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



129 



displacing the oxygen from laked ox blood with ferri-cyanide of 

 potassium, and measuring the amount of gas. The percentage 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 

 tube is then withdrawn, and tube C quickly closed with the finger to 



FIG. 129. Gowcr's haemoglobinometer. 



prevent the gas escaping. The tube is then inclined up and down about 

 a dozen times, so that the haemoglobin becomes saturated with CO. 



Distilled water is then added drop by drop from the dropping 

 pipette A, until the tint appears equal to the standard. After half a 

 minute read the percentage, and then add another drop or drops till 

 the tints appear just unequal. Read the percentage again, and take 

 the mean of the two readings as correct. In comparing the tints hold 

 the tubes against the skylight, and frequently change the tubes from 

 side to side. Many other forms of haemoglobinometer have been con- 

 trived, but in comparison with this instrument none of them are worth 

 notice. 



The number of Corpuscles in the Blood. The Thoma-Zeiss Haema- 

 cytometer consists of a counting chamber and an accurately calibrated 

 pipette. 



I 



