W" P^'" 



SPECIFIC GRAVITY 285 



are equal to one another, so that by this somewhat more complicated method 

 of examination we learn no more than may be more simply determined. 

 There are also tables from which we may read off directly the specific gravity 

 of the blood with a definite amount of hemoglobin, and vice versa. This 

 intimate dependence is clear without further explanation: The hemoglobin, 

 as the principal constituent of the red blood-cell, determines the greatest 

 fluctuation in the gravity of the total blood, especially since the fluid of the 

 blood is of an extraordinary constancy in its composition. Only when the 

 specific gravity of the blood serum becomes decidedly lighter than the normal 

 will the parallelism between hemoglobin and specific gravity of the total blood 

 be destroyed. 



Closely related to the estimation of the specific gravity are the quantitative 

 estimation of the total solids and the estimation of the amount of albumin 

 or nitrogen of the blood. Neither method has as yet been adopted in practice, 

 partly because they are much too diiBcult, and partly because they do not 

 enable us to form any opinion which we cannot otherwise arrive at much 

 more readily. It must be added that the result of the estimation of nitrogen 

 in some cases cannot be utilized at all, for, besides the hemoglobin and the 

 white blood-corpuscles, other nitrogen-containing substances, of other origin, 

 may be present in the blood and in an indefinite amount. In reviewing what 

 has been written in special works upon the subject regarding these methods 

 of investigation, we must say that they have added nothing distinctly new 

 to hematology. 



The investigations which have been made with the total blood have been 

 extended for scientific purposes to the individual constituent parts, also par- 

 ticularly to the estimation of the amount of albumin and of the specific 

 gravity. The separation of the two integral parts, blood-coepuscles and 

 SEEUM, may be inade in a simple manner either by sedimentation or centrifu- 

 gation. Material for investigation may be procured even from a few drops 

 of blood; it is sucked up into small glass tubes in which the serum, at the 

 latest in twenty-four hours, may be spontaneously expressed. 



As the most important result of these researches, it must be emphasized 

 that the serum in some pathologic conditions does not take part in the 

 changes of the total blood but retains its composition. Thus, according to 

 Grawitz, the serum in chlorosis and in progressive pernicious anemia does not 

 fake part, or to a very slight extent, in the hydremia of the total blood, and 

 invariably shows normal quantities of total solids. In chronic nephritis, the 

 hydremia of the total blood is chiefly attributed to the decided increase of 

 water in the serum. 



I shall mention still other methods of blood examination, although they 

 have not as yet been considered of importance in practice ; because it seems 

 advisable briefly to describe some conditions of which mention is occasionally 

 made. For, since the purpose of this article is the stimulation of more 

 frequent hematologic investigation in practice, we must consider not only 

 those methods which have been found of practical value, but those with which, 

 in spite of great efforts, little or nothing has been demonstrated either theoret- 

 ically or practically. 



