PRACTICAL EXERCISES 65 



puscles rather than to the pigment, and other 'oxygen-carriers' 

 e.g., fresh vegetable protoplasm, milk, seminal fluid, and pus will 

 cause the same colour. The test is chiefly of value as a negative 

 test. When the blue colour is not obtained, we have good evidence 

 that blood is absent. 



(4) Quantitative Estimation of Haemoglobin (a) By Fleischrs 

 Hczmometer (Fig. 15). Fill with distilled water that compartment a' 

 of the small cylinder (above the stage) which is over the tinted wedge. 

 Put a little distilled water into the other compartment a. Now prick 

 the finger and fill one of the small capillary tubes with blood. See 

 that none of the blood is smeared on the outside of the tube. Then 

 wash all the blood into the water in compartment a, and fill it to the 

 brim with distilled water. By means of the milled head T move the 



FIG. 15. FLEISCHL'S H^MOMETER. 



tinted wedge ^Ttill the depth of colour is the same in the two com- 

 partments. The percentage of the normal quantity of haemoglobin 

 is given by the graduated scale P. For example, if the reading is 

 90, the blood contains 90 per cent, of the normal amount ; if 100, it 

 contains the normal quantity. The observations should be made in 

 a dark room, the white surface S, arranged below the compartments 

 a and a, being illuminated by a lamp. Or the instrument may be 

 placed in a small box, lighted by a candle. It is best that each result 

 should be the mean of two readings, one just too large and the 

 other just too small. 



(b) Hoppe-Seyler's Method. Two parallel-sided glass troughs are 

 used. In one is put a standard solution of oxy-haemoglobin of known 

 strength, in the other a measured quantity of the blood to be tested. 

 The latter is diluted with water until its tint appears the same as that 



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