SPECTROSCOPIC EXAMINATION 287 



VI. VOLUME OF RED CELLS 



Some authors attach a certain value to the determination of the volume 

 of the red blood-cells in a definite amount of blood. For the correct estima- 

 tion of this various instruments have been invented, and either those in which 

 the blood-corpuscles are separated from the serum by centrifugation (" hema- 

 tohrit ") or those in which this occurs by spontaneous sedimentation, can be 

 employed. Every method should be rejected in which salt or a salt solution 

 is used to prevent the coagulation of the blood. For the volume of red 

 corpuscles remains uninfluenced only when it comes in contact with an isotonic 

 salt solution; as, however, particularly in pathological conditions, a special 

 concentration is isotonic for each kind of blood in each individual case, the 

 estimation of the volume would first depend upon a previous determination 

 of the isotonic salt solution; and such a difficult process can be of no use 

 in practice. 



The method which we owe to Koppe is very valuable because coagulation 

 is prevented in the centrifugal tubes of his hematokrit by the absolutely 

 smooth walls of the tubes. As the blood, therefore, remains unmixed we may 

 perhaps assume that, after complete centrifugation, the proper proportion of 

 plasma and cells as it exists in the blood-vessels is shown. 



If, however, the pathology of the blood is investigated by estimations of 

 volume, the figures obtained by these instruments show nothing that may be 

 looked upon as enriching our knowledge or promoting our understanding 

 of diseases of the blood; and I only refer to this method for the sake of 

 completeness, with the express statement that at present it cannot be consid- 

 ered a clinical method of investigation. 



VII. SPECTROSCOPIC EXAMINATION 



For certain methods of examination of the blood the use of the spectro- 

 scope must be understood, for in the recognition of various hemoglobin com- 

 binations which are characteristic of certain conditions, particularly of poison- 

 ing, the spectroscopic investigation of the blood is absolutely necessary and 

 enables us to reach conclusions not to be arrived at by the microscope or any 

 other methods. The principle of this method must be considered as under- 

 stood; but it may be mentioned that in qualitative investigations, as a rule, 

 a so-called pocket spectroscope is sufficient, and that it is well to place the 

 blood for examination in watery solutions of varying concentrations between 

 two plane parallel glasses. 



The determination of CO-Hb and of methemoglobin, the former occurring 

 in carbonic acid poisoning, the second in various forms of intoxication, par- 

 ticularly with potassium chlorate, is of the greatest practical importance. The 

 spectroscopic determination of methemoglobin, as may be noted from the 

 adjoining table, is possible by characteristic absorption lines (Fig. 16). (The 

 determination of CO-Hb is difficult on account of the similarity of the spec- 

 trum with that of 0-Hb. The differentiation is only certain when we observe 



