•22 THE BLOOD. 



may then unite again. The phenomenon is probably of a physical 

 kind: it will take place in blood that has stood for some hours" after 

 it has been drawn, and also when the globules are immersed in serum 

 in place of liquor sanguinis.* 



By processes, which need not liere be detailed, Vierordt and Welcker have esti- 

 mated the number of red coqjuscles in a cubic millimetre of hmnan blood. The 

 fomier assigns it at upwards of .5,000,000 ; the latter at 5,000,000 in the male, 

 and 4,500,000 in the female. 



Fi-. 12. 



Fig. 12. — Human Red Corpuscles (A) and Blood Cokpuscles op the Froo (B) placei> 



SIDE BY SIDE TO SHOW RELATIVE SIZE. 500 DiAMETERS. 



1, shows their broad surface ; 2, one seen edgeways ; 3, shows the eflfect of dilute 

 acetic acid ; the nucleus has become distinct (from Wagner). 



Like the mammalian blood-disks the large corpuscles of the frog and 

 salamander may be described as consisting of coloured matter and 

 stroma. They differ from them however in the possession of a more 

 solid particle of an oval shape which lies imbedded in the stroma. This 

 lias been long knov/n as the "nucleus," it is rather more than one-third 

 the length of the corpuscle. In the natural unaltered condition the 

 nucleus is seldom visible ; this is probably owing to the extreme 

 smoothness of its outline and the fact that it possesses very nearly the 

 same index of refraction as the rest of the corpuscle. For it may be 

 rendered visible, even under such circumstances, by the combined action 

 of watery vapour and carbonic acid upon the blood ; a precipitate (of 

 paraglobulin) is thus produced upon the nucleus, and its outline comes 

 into view ; on rcadmission of air the precipitate is re-dissolved, and 

 the nucleus again disappears (Strieker). 



The effect of most reagents is similar to that produced on human blood. 

 Water causes both stroma and nucleus to swell up by imbibition, the coloured 

 part bemg extracted at the same tune. A dilute solution of acetic acid in an 

 indifferent fluid also removes the colom-ing- matter. Init the stroma and nucleus 

 retain their shape, the last-mentioned body presenting a markedly granular 

 appearance (fig. 12. 8) ; if strong acetic acid be employed, the nucleus often 

 ;ic(iuires a reddish tint. Alkalies, on the other hand, even when veiy dilute, 

 rapidly destroy both corpuscle and nucleus. Various reagents added to ne\\-f.s 

 blood cause the coloured part of the coiiiuscles to become collected around the 

 nucleus, and to l)e more or less withdrawn from the stroma ; this is more especi- 

 ally the case with a two per cent, solution of l)oracic acid (Briicke) : the 

 coloured matter and nucleus may subsequently be altogether extruded from 

 the body of the corpuscle. 



For possible exjjlanations of this phenomenon tlie reader is referred to memoirs by 

 Lister (Phil. Trans., 1858), aud Nords (Proc. Roy. Soc. 1869). 



