SECT. 222.] 



FORMATION OF BLOOD-CKLLS. 



S3* 



Blood-corpuscles of a sheep 

 embryo, 3 J lines long. a. Dauhle 

 and triple nucleate:!, large, co- 

 loured, blood-globules, in dif- 

 ferent stages of division ; b. 

 large, round, coloured blood- 

 cells, one with its nucleus di- 

 viding; c. a smaller one. Mag- 

 nified 300 times. 



sheep embryo of 3.'; lines long, the most of them measured 0005'" 

 to o'Oo65'", but some only o - oo25'" to Fig.216. 



°' 00 35' " ■> m a human embryo, 4 lines 

 Long, they measured, according to Paget, 

 0"004'" to o - O07'". At first, these red, 

 nucleated corpuscles, along with their 

 colourless formative cells, constitute the 

 only elements of the blood. But many 

 of them soon commence to multiply by 

 partition, growing first into an elliptical 

 shape, some of them being even flattened, 

 and then being extremely like the blood- 

 corpuscles of amphibia. At this time the 

 cells are o'ooc/" in length, and o - oo4"' to 

 o , oo6" / in breadth ; they produce two, or 

 more rarely, three or four roundish nu- 

 clei, and then divide into as manv new 

 cells, through one or more constrictions. 

 As soon as the liver begins to grow, this multiplication of the 

 blood-cells in the entire mass of blood ceases, and soon, also (in 

 sheep embryoes of 1 1 lines), we lose all trace of their development 

 from the colourless, formative cells ; on the other hand, as Reiclievt 

 inferred, and as I have directly demonstrated, a very active for- 

 mation of blood-cells appears in the liver, the reason of which may 

 be found in the circumstance, that at this period all the blood of 

 the umbilical vein, by which the embryo is supplied with new 

 plastic materials, first flows into the liver, instead of into the 

 general circulation, as formerly. In the formation of cells which 

 henceforth goes on in the hepatic vessels, the multiplication of the 

 blood-corpuscles, by partition of themselves, retires more and more 

 into the background. Instead of this process, colourless, nucleated 

 cells are formed in the blood of the liver, measuring, on an average, 

 o - oo3'" to 0*004"' (o"OOi5"' to o - oo6'" at the extremes), and these 

 become transformed, for the most part in the liver, into coloured, 

 nucleated blood-cells by the formation of colouring matter in the 

 cell-contents ; this change takes place either immediately or after 

 the colourless cells have multiplied in the way already described 

 for the primitive red corpuscles. The place of origin of these 

 colourless cells (the first proper white blood-corpuscles) is not yet 

 ascertained ; but I am of opinion that they are produced in great 

 measure by the spleen, for it is certain that in the later half 

 of foetal life, this organ does transmit numerous colourless cells 



m m 2 



