190 THE BLOOD 



As a disturbance in the relationship of these two factors is most 

 likely to result in consequence of pathological conditions, it is essential 

 to be in possession of a quick and accurate method for the quantitative 

 determination of this substance. It is quite true that a knowledge of 

 the hemoglobin content of the blood frequently facilitates the diag- 

 nosis, but, as has just been emphasized, this value must first be brought 

 into relation with the number of the red cells, otherwise it may give 

 rise to very erroneous deductions regarding the general condition of 

 the blood. Two methods have been advocated for the determination 

 of hemoglobin. One of these has been described by Welker and Hoppe- 

 Seyler, 1 and is known as the chronometric. The other, described by 

 Vierordt and Glan, 2 is known as the spectrophotometric. The various 

 modifications of the first take the normal quantity of hemoglobin to 

 be 100 per cent, and the normal number of the red corpuscles (5,000,000 

 per cu. mm.) also 100 per cent. The color exhibited by a sample of 

 blood of this quality is regarded as unity; this standard being obtained 

 by employing the percentage of hemoglobin as the numerator and the 

 percentage of the corpuscles as the denominator. Thus, if the num- 

 ber of the red cells remains the same, while their hemoglobin content 

 is diminished, the color index becomes smaller than 1. A reduction 



80 



of the hemoglobin to 80 per cent, gives an index of 7 - = 0.8, which 



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Q 



value implies that the different corpuscles carry only y^ of the normal 



quantity of hemoglobin. Under certain pathological conditions the 

 decrease in the percentage of hemoglobin is often associated with a 

 diminution in the percentage of the corpuscles; moreover, the reduc- 

 tions may or may not be equally great in the tjvo cases. If they are 

 equal, the color index is 1, and if they are not, the latter is either smaller 



or larger than 1. To illustrate, assuming that the percentage of 



fin 

 hemoglobin is 60 and the percentage of corpuscles 80, the index : ^ 



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0.75, suggests that the different corpuscles are loaded with only three- 

 fourths of the amount of hemoglobin ordinarily carried by them. 

 And again, a percentage of hemoglobin of 60 and a percentage of red 



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cells of 50 gives the index :^r = 1.2, which indicates that the hemo- 



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globin content of the individual corpuscles is greater than normal. 



The principle involved in this method is the following: If two solutions in 

 identical receptacles are exposed to the same source of light and exhibit the same 

 color, their content in coloring matter must be the same. Hence, it should be 

 possible to prepare a solution of hemoglobin of known concentration and to deter- 

 mine the hemoglobin content of other samples of blood by simply comparing them 

 with this standard solution. But, as standard solutions of this kind cannot always 

 be easily kept, the attempt was made at an early date to find a more permanent 



1 Zeitschr. fur physiol. Chemie, xv, xvi, xxi, 1891, 1892, and 1896. 



2 Poggend. Ann., 1877. 



