220 BLOOD. 



to give the correct relation. It was chiefly by the three fol- 

 lowing methods that Schmidt was enabled to determine this 

 factor : 



1. He determined, by micrometrical measurement, the dimi- 

 nution which the red blood-cells undergo on drying. If they are 

 dried under circumstances which admit of an uniform evaporation 

 of water in all directions, Schmidt finds that they undergo a 

 constant diminution of volume, amounting to 68 or 69^ of that of 

 the fresh cells ; hence the latter contain about 68 or 69 parts of 

 water to 32 or 31 of solid substances, or nearly four times as much 

 of solid constituents as is dissolved in the plasma. 



2. After Schmidt had convinced himself that the quantities of 

 serum expressed from the clot at different times had the same 

 density and the same composition, he investigated by the micro- 

 scope the volumetric relation existing between the blood-cells and 

 the intercellular substance (fibrin + serum) in the clot in its 

 most contracted state; and ascertained that in 100 volumes of clot, 

 there are at the most 20 volumes of intercellular substance, or 

 one-fifth of the whole volume ; if, therefore, the four-fifths of the 

 volume of the blood-corpuscles in the clot be compared with the 

 volume of the whole blood (clot + serum), we find that the blood 

 must contain at least 40, by volume, of fresh cells; Schmidt 

 moreover found, in further comparisons of this kind, that, as a 

 general rule, the blood contains a larger volume of blood-cells, and 

 that it may rise to 53 or 54-g- of the whole volume. 



3. The third equation of condition which Schmidt applied to 

 the determination of this coefficient, depends on the comparison of 

 the unequally divided mineral constituents in the clot and serum. 

 It has been already fully demonstrated that potash-salts and phos- 

 phates predominate in the blood-cells a point on which any one 

 may easily convince himself by comparing an accurately made ash- 

 analysis of the clot or of the cruor (if the fibrin has been removed) 

 with that of the corresponding serum. Since, unfortunately, the 

 serum is never entirely free from phosphates and potash-salts, while 

 the blood-corpuscles are never entirely free from alkaline chlorides 

 and soda-salts (in the analyses made by Schmidt, and in accordance 

 with his method), this might appear to be the best check on the 

 coefficient established by Schmidt ; but unfortunately it cannot be 

 used to ascertain, in a special case, whether Schmidt's calculation of 

 the relation of the cells to the intercellular fluid be correct. If 

 there were a substance to be detected in the serum, so peculiar, 

 and so easily separable and determinable quantitatively, by chemical 

 means, as the heematin in the blood-corpuscles, then from the 



