CHAP. IV.] THE BLOOD. METHODS OF RESEARCH. 183 



By adding then 1520 c.c. of water to 400 c.c. of the diluted blood we 

 should obtain 1920 c.c. of a solution equal in shade and intensity of colour 

 to the standard solution of haemoglobin. But on analysis the latter was 

 found to contain in 100 c.c. 0*145 grms. of haemoglobin; we now have the 

 data for determining the total quantity of haemoglobin in the diluted 

 blood : 



100 : 0-145 :: 1920 : x 



x 2784 grms. 



But as this quantity of haemoglobin was derived from 20*186 grms. 

 of blood, the amount contained in 100 parts is found thus: 

 20-186 : 2-784 :: 100 : x 

 x= 13*79 grins. 



This method gives most accurate results ; its use was formerly 

 deprecated, inasmuch as it requires solution of pure oxy-haemoglobin, 

 which cannot easily be prepared except in the depth of winter, and 

 which when prepared will not keep more than a few days in the 

 open air. Hoppe-Seyler has however shewn that solutioDS of 

 pure haemoglobin in sealed glass tubes may be kept indefinitely 

 without the haemoglobin undergoing decomposition. Nothing can 

 therefore be easier than to make a stock of pure solution of oxy- 4 

 haemoglobin in winter and store it in a large number of sealed 

 glass tubes for use during the succeeding year. The oxy-haemoglo- 

 bin is soon reduced to haemoglobin, but, after that, resists all further 

 change. When the tubes are opened the solution rapidly absorbs 

 oxjgen and a solution of oxy-haemoglobin is obtained. 



Instead -of employing a standard solution of oxy-haemoglobin, we 

 may, as suggested by Kajewsky 1 , use, as a standard, a solution of 

 picro-carminate of ammonia, corresponding in tint to a solution of 

 haemoglobin of known strength. A solution of picro-carminate, if per- 

 fectly neutral, may be preserved in stoppered bottles for long periods ; 

 according to Malassez 2 it may be kept indefinitely. 



The following is the method of preparing a solution of picro-carminate of 

 ammonia. 



Take 100 c.c. of a saturated solution of picric acid. Prepare an 

 ammoniacal solution of carmine by dissolving 1 grm. in a few c.c. of water, 

 with the aid of an excess of ammonia and heat. Boil the picric acid, and 

 when boiling add the carmine solution. Evaporate the mixture to dryness, 

 and dissolve the residue in 100 c.c. of water, and filter. A clear solution 

 ought to be obtained ; if not, add some more ammonia, evaporate, and then 

 dissolve as before 3 . This solution is now added, little by little, to a 

 mixture of equal parts of water holding a little phenol in solution, and of 

 glycerine, until the tint, observed in a haematinometer, is exactly similar to 



1 A. Rajewsky, "Zur Frage iiber die quantitative Bestimmung des Hamoglobin- 

 gehaltes im Blut.'" Pfluger's Archiv, Vol. xn., p. 70. 



2 Malassez, " Sur les diverges methodes de dosage de I'hemoglobine et sur un 

 nouveau colorimetre." Archives de Physiologic, 1877, pp. 1 13. 



3 Rutherford, Outlines of Practical Histology, p. 173. 



