216 BLOOD. 



very unequally distributed in the clot from above downwards. In 

 many cases it is better to separate the serum from the cruor, 

 according to Popp's method, than from the clot according to the 

 method of the French chemists. This separation of the serum 

 from the sunk corpuscles by any method is however, in most 

 cases, the most uncertain part of the analysis ; for in drawing or 

 pouring off the fluid portion from the clot, it rarely happens that 

 the serum is obtained perfectly free from blood-corpuscles, or the 

 clot perfectly free from serum, independently of the quantity which 

 is enclosed. 



Although, however, all authors have been compelled to admit 

 that this mode of determining the dry corpuscles can have no abso- 

 lute value, it has been generally regarded as perfectly available 

 and sufficient for comparative analyses of the blood ; but we must 

 remember with what very different power the fibrin contracts in 

 the clot in different diseases ; a very dense clot will enclose far 

 less serum than a very loose gelatinous one; and we do not take 

 into account, that sediments of blood-corpuscles often occur 

 external to the clot : further the serum obtained from the blood- 

 corpuscles occurs in no definite proportion, since the quantity 

 of serum remaining mixed with the corpuscles is less dependent 

 on the manipulation of the operator than on accident. 



Simon* struck upon a method of finding the quantity of the 

 blood-corpuscles directly, which however is altogether wanting in 

 accuracy. He coagulated whipped blood by the application of 

 heat, stirring or shaking it the whole time, and then extracting the 

 coagulum with ether and boiling alcohol : he thought that boiling 

 alcohol left the albumen of the serum in a state of purity, and 

 dissolved the constituents of the blood-corpuscles together with 

 the salts and extractive matters of the serum ; after the 

 evaporation of the alcoholic solutions, the residue was extracted 

 with cold aqueous spirit which, as Simon appeared to believe, 

 left undissolved all the constituents of the blood-corpuscles, while 

 it dissolved the non-coagulable matters of the serum. This method 

 presents so many imperfections that one only wonders how Simon's 

 blood-analyses should coincide so tolerably well with those of 

 other experimenters. In illustration of the utter unfitness of this 

 method it may suffice to mention, that two analyses of one and the 

 same blood, made according to Simon's directions, would never by 

 any chance coincide. This method, in consequence of its minuteness 

 of detail, has never been adopted in large series of blood-analyses. 

 * Med. Chem. Bd. 2, S. 83 [or English Translation, vol. 1, p. 175]. 



