PRACTICAL EXERCISES 69 



considered chiefly of value as a negative test. When the blue colour 

 is not obtained, we have good evidence that blood is absent. But, 

 according to Buckmaster, if the precaution of first boiling the liquid 

 suspected to contain blood be adopted, it is also a good positive test. 

 (4) Quantitative Estimation of Haemoglobin (a) By Haldane's 

 Modification of Gowers' Hcemoglobinometer. Place in the graduated 

 tube B (Fig. 17) an amount of water less than will ultimately be 

 required to dilute the blood to 'the required tint. Puncture the 

 finger or lobe of the ear with one of the small lancets in F, and fill 

 the capillary pipette D to a little beyond the mark 20. Wipe the 

 point of the pipette and dab it on a piece of filter-paper till the 

 blood stands exactly at the mark. Blow the blood into the water 

 in B, and rinse the pipette with the water. Attach the cap of tube 

 G to a gas-burner. Introduce the rubber tube into B nearly to the 

 level of the water, and allow gas to pass for a few seconds. With- 



FIG. 18. FLEISCHL'S H^MOMETER. 



draw the tube while the gas is still passing. Immediately close the 

 end of B with the finger, and move the tube so that the liquid 

 passes from end to end of it at least a dozen times, to saturate the 

 haemoglobin with carbonic oxide. While this is being done, the 

 tube should be held in a cloth, otherwise it will become heated, and 

 liquid will spurt out when the finger is removed. Water is now 

 added drop by drop with the pipette stopper of the bottle E, which 

 is used for holding the water, the tube being inverted after each 

 addition, till the tint in B is the same as that in A. In comparing 

 the tubes, they should be held against the light from the sky or 

 from an opal glass lamp-shade. It is necessary to transpose the 

 tubes repeatedly. The level at which the tints are equal is read 

 off on B half a minute after the addition of the last drop of water. 

 Water is now again added by drops till the tint in B is just notice- 

 ably weaker than in A, and the mean of the two readings is taken. 



