6o 



PRACTICAL PHYSIOLOGY. 



[VII. 



('•.) Distilled water is then added drop by drop (from the pipette 

 stopper of a bottle (A) suppUed for that purpose) until the tint of 

 the dilution is the same as that of the standard. The amount of 

 water which has been added {i.e., the degree of dilution) indicates 

 the amount of haemoglobin. 



" Since average normal blood yields the tint of the standard at 

 1 00° of dilution, the number of degrees of dilution necessary to 



Fia. 35.— -4. Pipette bottle for distilled water ; B. Capillary pipette ; C. Graduated tube. 

 D. Tube with standard dilution ; F. Lancet for pricking the finger. 



obtain the same tint with a given specimen of blood is the per- 

 centage proportion of the haemoglobin contained in it, compared to 

 the normal. For instance, the 20 c.mm. of blood from a patient 

 with anaemia gave the standard tint of 30" of dilution. Hence it 

 contained only 30 per cent, of the normal quantity of haemoglobin. 

 By ascertaining with the haemacytometer the corpuscular richness of 

 the blood we are able to compare the two. A fraction of which 

 the numerator is the percentage of haemoglobin, and the denomina- 

 tor the percentage of corpuscles, gives at once the average value per 

 corpuscle. Thus the blood mentioned above containing 30 per cent, 

 of haemoglobin contained 60 per cent, of corpuscles; hence the 

 average value of each corpuscle was f^ or half of the normal. 

 Variations in the amount of haemoglobin may be recorded on the 

 same chart as that employed for the corpuscles." 



" In using the instrument, the tint may be estimated by holding 

 the tubes between the eye and the window, or by placing a piece 

 of white paper behind the tubes ; the former is perhaps the best 



