DERIVATIVES OF HEMOGLOBIN. 45 



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. 

 In practice it will be found that, during 6 or 8 degrees of dilu- 

 tion, it is difficult to distinguish a difference between the tint of 

 the tubes. It is therefore necessary to note the degree at which 

 the colour of the dilution ceases to be deeper than the standard, 

 and also that at which it is distinctly paler. The degree midway 

 between these two will represent the haemoglobin percentage." 



9. Fleischl's Hsemometer. This apparatus (Fig. 9) consists of 



Fig. 9. Fleischl's Hsemometer. 



a horse-shoe stand with a pillar bearing a reflecting surface (S) 

 and a platform. Under the table or platform is a slot carrying a 

 glass wedge stained red (K), and moved by a wheel (R). On the 

 platform (M) is a small cylindrical vessel divided into two com- 

 partments (a and a') by a vertical septum. In one compart- 

 ment is placed pure water, and in the other the blood to be 

 investigated. A scale (P) on the slot of the instrument enables 

 one to read off directly the percentage of haemoglobin. 



(a.) Fill with a pipette the compartment (a') over the wedge 

 with distilled water, and see that the surface of the water is 



