CHAP. II.] THE BLOOD. 79 



whilst the total number of corpuscles amounts to about 22,500 

 milliards 1 . Admitting the superficies of each blood corpuscle to be 

 j^^ths of a millimetre square, then the total superficies of the blood 

 corpuscles of men would amount to about 2880 square metres, i.e. 

 to the area of a square, each of whose sides is about 53 '66 metres 

 long. 



Density and weight of the coloured corpuscles. According to C. 

 Schmidt the coloured corpuscles of the blood have a specific gravity 

 of 1089, and according to Welcker of 1105. 



The student may feel some curiosity to know the method 

 which was followed in making these determinations, and it may be 

 said at once that the above results were obtained by calculation, and 

 that their correctness depends upon the reliability of several data. 

 Assuming that we know 1st the weight of the moist corpuscles in 

 a known volume of blood, 2nd the specific gravity of the same 

 blood defibrinated, 3rd the specific gravity of the serum, and if 

 we further assume that the specific gravity of the serum does not 

 differ sensibly from that of the plasma, we have all the data required. 

 Thus to take an example from Lehmann's Physiological Chemistry : 

 If we assume, for instance, that a specimen of blood contains 496 parts 

 of moist cells per 1000, besides 4 parts of fibrin, that the specific gravity 

 of the serum is 1028, and that of the defibrinated blood 1057*4, 

 then we may very readily determine the density of the blood cells by 

 the following considerations : 



1000 4 = 996 parts of defibrinated blood occupy the space of 



941'93 parts of water, 



500 parts of serum ... 486'38 



hence 496 parts of blood cells ... 45 5 '5 5 parts of water. 



455 55 : 496 :: 1000 : 1088'8. 



The density of the blood cells in this specimen of blood must there- 

 fore be 1088'8 2 . It must be remarked, that the weight of the moist 

 blood corpuscles can only be determined in an approximately accurate 

 manner. 



Welcker has calculated the approximate weight of the coloured 

 blood corpuscle to be O'OOOOS or TGiwinr ths of a milligramme 3 . 



Summary of the' composition of the coloured corpuscles. 



Before describing the principal organic and mineral constituents of 

 the red blood corpuscles it will be convenient to place before the reader 

 the following analytical data. 



1 A milliard (Fr.) is one thousand millions. 



2 Lehmann, Physiological Chemistry, Vol. n. p. 163. 



3 Welcker, loc. cit. p. 274. 



