THE BLOOD. 81 



give the haemin crystals with glacial acetic acid. Another part of 

 the alkaline solution shows, after the addition of STOKE'S reduc- 

 tion liquid, the absorption-bands of haemochromogen in alkaline 

 solution. 



The methods proposed for the quantitative estimation of the 

 blood-coloring matters are partly chemical and partly physical. 



Among the chemical methods to be mentioned is the ashing of the blood 

 and the determination of the amount of iron contained therein, from which 

 the amount of haemoglobin may be calculated. Another method consists in 

 first saturating the blood completely with oxygen. Now pump out thor- 

 oughly this oxygen, and calculate from the amount of oxygen the amount of 

 haemoglobin present (GREHANT and QUINQUAUD). None of these methods is 

 reliable. 



The physical methods consist either in a colorimetric or a spec- 

 troscopic investigation. 



The principle of HOPPE-SEYLER'S colorimetric method is that a 

 measured quantity of blood is diluted with an exactly measured 

 quantity of water until the diluted blood solution has the same 

 color as a pure oxyhaemoglobin solution of a known strength. The 

 amount of coloring matter present in the undiluted blood may be 

 easily calculated from the degree of dilution. In the colorimetric 

 testing we use a glass vessel with parallel sides containing a layer 

 of liquid 1 cm. thick (haematinometer of HOPPE-SEYLER). The 

 method is good, and the inconvenience that the normal solution 

 of oxyhaemoglobin does not keep for any length of time without de- 

 composing may be prevented by preserving the solution in sealed 

 tubes. The oxyhaamoglobin is gradually reduced to a haemoglobin 

 solution which may be kept for years, and when required for use it 

 is converted into an oxyhaemoglobin solution by aerating. A few 

 observers (RAJEWSKY, LESSER" MALLASSEZ) have tried to replace 

 the oxyhaemoglobin solution by a solution of picrocarmin. 



The quantitative estimation of the blood-coloring matters by 

 means of the spectroscope may be done in different ways, but at 

 the present time the spectrophotometric method is chiefly used, and 

 this seems to be the most reliable. This method is based on the 

 fact that the extinction coefficient of a colored liquid for a certain 

 region of the spectrum is directly proportional to the concentra- 

 tion, so that G : E = C t : E l , when C and C l represent the differ- 

 ent concentrations and E and E. the corresponding coefficient of 



C C 



extinction. From the equation ^ = it follows that for one and 



Jii Jt l 



the same coloring matter this relation, which is called the absorp- 

 tion ratio, must be constant. If the absorption ratio is represented 

 by A, the determined extinction coefficient by E, and the concen- 



