202 THE BLOOD. 



The determination of the percentage of haemoglobin which 

 is required to j'ieid the spectroscopic result above described, 

 is accomplished by introducing a concentrated solution of a 

 known weight of pure haemoglobin crystals into a glass cham- 

 ber (so-called haematinometer), of which the parallel sides are 

 one centimetre from each other. The chamber is then placed 

 in front of the slit of the spectroscope, the source of light 

 being a paraffin lamp. Distilled water is then carefully added 

 from a finely divided burette, so long as all of the spectrum is 

 extinguished excepting the red. The moment that the green 

 begins to appear, the operation is ended. The volume of the 

 diluted solution is determined ; and the exact conditions, viz., 

 the distance of the lamp and chamber, and the widtli of the 

 slit, are carefully noted. The percentage of haemoglobin con- 

 tained in the solution is that at which, under the given condi- 

 tions, complete absorption of the green takes place. It may 

 be designated k. 



In order to ascertain the percentage of haemoglobin con- 

 tained in any given specimen of blood, all that is required is 

 to repeat the process just described. A small quantity of 

 fresh blood, which has been well ngitated with air and defibri- 

 nated, is introduced into a finely graduated small pipette, 

 from which exactly one centimetre is delivered into the glass 

 chamber above mentioned, and diluted before the slit of the 

 spectroscope (the liquid being carefully stirred after each 

 addition) until the green begins to appear. At this moment 

 the liquid contains a percentage of haemoglobin equal to k. 

 If the volume of distilled water including the centimetre 

 originally added, be designated c, and the original volume of 

 blood 6, the percentage of haemoglobin which the blood con- 

 tains is readily calculated according to the formula 



: -~- Whence, if the quantity of blood used, as above 



iC 



supposed, be one centimetre, we have x=.lc (1 + c). 



25. Determination of the Quantity of Haemoglobin 

 in Blood, by the Estimation of its Iron. Assuming 

 that haemoglobin contains 0.42 per cent, of iron, and that the 

 whole of the iron of the blood is contained in its coloring 

 matter, it is evident that if the percentage of iron existing in 

 any quantity of blood is known, the percentage of haemoglobin 

 can be readily calculated. Although the process has disad- 

 vantages as compared with that last described, both as regards 

 the time required for carrying it out, and the accuracy of the 

 results, it cannot be omitted, as, under many circumstances. 

 (V. f/., when the blood to be investigated is not perfectly fresh), 

 the spectroscopic method is inapplicable. To ascertain the 

 proportion of iron in blood, a weighed or measured quantity 

 of the liquid must be incinerated. The ash must then be dis- 



