CHEMICAL BASTS OF THE ANIMAL BODY. 225 



the absorption of carbon-dioxide is independent of the simultaneous 

 presence of oxygen 1 . 



The accurate quantitative determination of the amount of haemoglobin in any 

 given solution is a matter of extreme importance not merely in connection with 

 several of the statements contained in the preceding description of haemoglobin and 

 its compounds with gases, but also in many investigations which turn on the 

 varying amounts of this substance under different experimental conditions, and 

 further for clinical purposes. It may therefore not be out of place to describe 

 briefly the principles on which the determinations are based, referring the reader to 

 special works for the details of the respective processes. 



The methods employed fall under two categories : chemical and physical. 



1. Chemical, a. The amount of iron present in 100 parts of haemoglobin has 

 been frequently determined for the blood of various animals. It may be stated to 

 be about -43 '45 p.c. Hence if a solution of this substance be evaporated to 

 dryness and the residue incinerated, the amount of haemoglobin may be inferred 

 from the amount of iron existing as oxide of iron, in this residue 2 . b. Since the 

 volume of oxygen which unites with a given quantity of haemoglobin is known with 

 considerable accuracy (but see above p. 222), the amount of this substance may be 

 determined by saturating its solution with oxygen and then estimating the volume 

 of the gas which is united to the haemoglobin. The determination is made either 

 by extracting the oxygen with a mercurial pump or displacing it by carbon-monoxide 

 or estimating it in the solution by a volumetric process with sodium sulphite and 

 indigo 3 . These methods are inferior to the following. 



2. Physical. These may be again divided into two; colorimetric and spectro- 

 photometric. 



(i) Colorimetric method. The principle of this method may be briefly stated as 

 follows. A standard solution of haemoglobin is prepared from pure crystals of the 

 substance. The tint of the solution in which the haemoglobin is to be determined 

 is then compared with that of the standard solution : if it is not the same when 

 examined under the same conditions, it must be equalised by either of the methods 

 to be next described and from the operations necessary to produce equality of tint 

 the relative concentrations of the two solutions may be inferred and hence the 

 absolute concentration of the unknown solution. The methods more usually 

 employed consist either in diluting one or the other of the solutions until their tint 

 is the same when examined in layers of equal thickness (Hoppe-Seyler) 4 or else in 

 determining the different thicknesses of the fluid layer of each which exhibits the 

 same tint (Duboscq). Since in the latter case the concentrations of the two 

 solutions are inversely proportional to the thicknesses of their layers when their 

 tint is the same the amount of haemoglobin in the solution of unknown strength 

 can be at once inferred 5 . For clinical purposes Gower's haemoglobinometer is 



1 Skandinav. Arch. f. PhysioL Bd. in. (1891), S. 62. 



2 Pelouze, Compt. Rend. T. i. (1865), p. 880. 



3 Grlhant, Compt. Rend. T. LXXV. (1872), p. 495. Quinquaud, Ibid. T. LXXVI. 

 p. 1489. Schiitzenberger et Kisler, Ibid. p. 440. 



4 Hdbch. d. physiol. pathol.-chem. Anal. Aufl. 5 (1883), S. 435. 



5 For a description of Duboscq's and other apparatus see G. u. H. Kriiss, 

 Kolorimetrie u. quant. Spektralanal. 1891, S. 7 et seq. This work gives a most 

 excellent account of the best physical methods employed for the determination of 

 colouring substances in solution. A useful review of methods up to date (1882), is 

 given by Lambling, "Des precedes de dosage de I'hemoglobine," Nancy, 1882. Cf. 

 later E. von Fleischl, Med. Jahrb. 1885, S. 425. Malassez, Arch. d. Physiol. 1886, 

 p. 257. 



