184 DETERMINATION OF HAEMOGLOBIN. [BOOK I. 



that of a standard solution of haemoglobin. As the picro-carminate has a 

 yellower shade than blood, it is advisable to add to it a small quantity of a 

 perfectly neutral solution of carmine. 



2. Preyer's This method requires (1) at least one haematino- 



meter, (2) a spectroscope, (.3) a steady light, (4) a standard 

 solution of haemoglobin, (5) a finely-divided burette. 



The haematinometer being placed between the luminous source 

 and the spectroscope, a strong solution of crystallized oxy-haemoglobin 

 in water is poured into it. If the solution be very strong, as was 

 mentioned at p. 97, only the red rays will pass. Water is now 

 added very gradually from the burette, until the first gleam of green 

 between E and F, and close to b, is perceived. In order to make the 

 appreciation of this more easy, the experiment is conducted in a 

 darkened room, and the lamp is furnished with a shade (as in Fig. 18) 

 which only allows the rays of light to proceed in the direction of the 

 spectroscope. The amount of haemoglobin in the standard solution 

 is now ascertained as in Hoppe-Seyler's method, by evaporating a 

 known volume to dryness. (Preyer has found that when examined in 

 a haematinometer of which the sides are 1 centimetre apart, a 

 solution of haemoglobin containing 0'8 grms. of the substance per 

 cent, just allows a narrow band of green close to b to appear.) 



About 0'5 c.c. of the blood, of which the amount of haemoglobin is 

 to be determined, is now poured into a haematinometer, and water 

 added to it from a burette until, when examined under exactly the 

 same circumstances as the standard solution, the green close to b just 

 appears. The amount of water added must be very precisely 

 measured. The amount of haemoglobin contained in the blood is 

 then found by the following equation : 



Hb(e + s) 



where Hb is the weight of haemoglobin contained in 100 c.c. of the 

 standard solution, e the volume of water added to the blood analyzed, 

 and s the volume of the latter. 



Dr cowers' The tint of the dilution of a given volume of blood 



toe SJL fOI> with distilled water is ta ken as the index to the amount 

 estimation of ^ haemoglobin. The distilled water rapidly dissolves 

 Haemogio- out all the haemoglobin, as is shewn by the fact that 

 bin 1 . the tint of the dilution undergoes no change on 



standing. The colour of a dilution of average normal blood one 

 hundred times is taken as the standard. The quantity of haemoglobin 

 is indicated by the amount of distilled water needed to obtain the 

 tint with the same volume of blood under examination as was taken 

 of the standard. On account of the instability of a standard dilution 

 of blood, tinted glycerine-jelly is employed instead. This is perfectly 

 stable, and by means of carmine and picro-carmine the exact tint of 

 diluted blood can be obtained. 



1 See "Report of the Meeting of the Clinical Society," the Lancet n. 1878, p. 822. 



