METHODS OF ANALYSIS. 215 



water in the clot probably stands in a near ratio to that of the 

 serum, Prevost and Dumas unquestionably believed that they 

 were most nearly approximating to the true ratio, when they re- 

 garded all the water found in the clot as pertaining to the serum, 

 and calculated accordingly the amount of the solid constituents of 

 the serum contained in the dry clot, the amount of fibrin being 

 previously deducted. 



Since the whole of this calculation depends on a mere simple 

 proportion it would be quite superfluous to enter into further 

 particulars regarding it. 



I cannot imagine, as C. Schmidt appears to assume, that 

 Prevost and Dumas actually believed that all the water of the clot 

 depended only on the serum, but I think it more than probable 

 that they took the view which we have already described. Since 

 the quantity of the serum enclosed in the clot could not be 

 absolutely determined, and as there was no available means of 

 estimating it, the only alternatives that remained for them were, 

 either to calculate all the water of the clot (after deducting the 

 fibrin) as belonging to the blood-corpuscles alone, or as belonging 

 to the serum alone ; and they chose the latter. Neither they nor 

 any of their followers have supposed that either of these views was 

 not decidedly erroneous ; they, as a matter of course, chose that 

 which obviously led to the smaller error. Von Bibra seems, 

 therefore, to have fallen into a mistake, in believing that by dis- 

 regarding the serum contained in the clot, he could diminish the 

 error of these chemists. 



The modifications of this method which other experimentalists, 

 namely Becquerel and Rodier, and Popp, have adopted, all retain 

 the same error to which we directed attention in speaking of the 

 plan originally made use of by Prevost and Dumas ; the former 

 determined the solid residue of the defibrinated blood, and 

 deducted from this the solid residue of the serum which they 

 calculated from the amount of water (the solid residue being 

 determined from a separate analysis of the serum). Popp analysed 

 the serum that separated from defibrinated blood, and then the 

 cruor which was formed under this serum. These modifications, 

 although not essential, are undoubted improvements on the 

 original method; for it would be folly to attempt the impossibility 

 of thoroughly drying the clot, as it is obtained from the coagulation 

 of the blood ; if, however, we take a portion of the clot for the 

 determination of the solid residue, we must at all events adopt the 

 caution of analysing a vertical section of it, since the corpuscles are 



