ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



87 



tube is then withdrawn, and tube C quickly closed with the finger to 

 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. The average percentage of woman's blood is 11 per cent., and 

 that of children's blood 13 per cent, below the average of adult men. 



0.100mm. 

 1 qmm,. 



C. Zeiss 

 Jena. 



FIG. 88. The Thoma-Zeiss haemacytometer. 



Therefore, in calculating the percentage for women add about J, and 

 for children about T ^ to the percentage found. Many other forms 

 of haemoglobinometer have been contrived, 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. 



The finger behind the nail is cleaned with alcohol and ether, and a 

 drop of blood is drawn by the stab of a lancet-shaped needle. The 

 finger should not be constricted by a ligature during this operation. 

 The point of the pipette is placed in the drop, and the blood is 

 aspirated as far as the mark 1. The traces of blood on the point 

 of the pipette are then removed, and the pipette is dipped into 

 Hay em's fluid. 1 



1 Sodium chloride, g. 2 ; sodium sulphate, g. 10 ; corrosive sublimate, g. 1 ; 



water, g. 400. 



