

NUMBER OF THE RED CORPUSCLES. 383 



the proportion of the radius to the height of which was 

 estimated to correspond with the dimensions of the blood cor- 

 puscles; and by scooping out the surface, and rounding off the 

 edge, he obtained a curvature of the surface, which, to the eye (!) 

 was similar to that of the blood corpuscles (compare fig. 67). 

 He thus determined the mean volume of human blood cor- 

 puscles to be 0*000,000,072,217 of a cubic millimeter. Welcker, 

 moreover, carefully lined the interior of this model, which was 

 5,000 times larger than the corpuscles, with paper of uniform 

 thickness, then weighed the paper used, and compared this 

 with the weight of a known superficial measure of the same 

 paper. From the data thus obtained he estimated that the 

 superficies presented by a blood corpuscle amounts to 0*0,001,280 

 square millimeter. It is sufficiently obvious that these num- 

 bers have only a coarsely approximative value. 



NUMBER OF THE RED CORPUSCLES. 



Estimates of the number of the corpuscles have also been 

 undertaken with the microscope. This method was suggested 

 by Vierordt, and has been modified by Welcker.* 



Their direct enumeration may be accomplished in the 

 following way : 



A measured volume of blood is diffused as equably as possible 

 in a thousand times its volume of an indifferent fluid (six 

 grammes of Na. Cl. in one litre of water, according to Welcker), 

 a small quantity of the mixture is taken up in a capillary 

 tube of known calibre, and the length of the thread of fluid 

 is estimated under the microscope by means of a micrometer. 

 When the contents of the tubule have thus been ascertained, 

 they are quickly distributed with a little solution of gum 

 upon a slide, and the whole is allowed to dry. The prepara- 

 tion is covered with a micrometer divided into squares, and 

 the corpuscles in the several squares can then be successively 

 counted. In one experiment Vierordt used 0'0005 0*0008 cubic 



* VieTor&t,ArchivfurPhysioL Heilkunde, Band xi., pp. 26, 327, 854; 

 xiii., p. 259 ; Grundriss der Physiol, 3. Auflage, 1824, pp. 8, 9. Welcker, 

 PragerViertel/ahreschnft.Tta,nd.xliv.,-p.6()', und Zeitschrift fur rationelh 

 Medicin, 3 R., Band xx., p. 280. 



