SECT. 222.] CORPUSCLES BEFORE AND AFTER BIRTH. ^Jj 



mass of the blood, they are not more numerous than the lymph- 

 globules in the blood of the adult. In the human embryo, it has 

 not yet been ascertained at what period the nucleated, coloured 

 cells become more scanty and disappear; but Paget has observed 

 them in considerable numbers, in one case in an embryo of five 

 months. — The blood of the more advanced embryo of mammalia 

 contains large numbers of colourless cells besides the red cor- 

 puscles, and these are often equal in number to the coloured cells, 

 and are found not only in the liver, but in the blood of other 

 organs also. The chief part of these colourless cells is undoubtedly 

 derived from the spleen and the liver; in the sheep's embryo, 

 thirteen inches long, one-third of the total blood-cells of the liver 

 are found to be of the colourless sort, with a few of the nucleated 

 red corpuscles ; in the later periods of embryonic life, many of 

 these colourless cells may also come from the lymph. It is un- 

 determined whether these later cells also become transformed into 

 coloured corpuscles, and all that we can afiirm concerning them is, 

 that the stages of transition, which are so frequently met with in 

 the blood of the liver and spleen (both in the white and in the 

 nucleated red corpuscles), are entirely absent in the blood of the 

 remainder of the body. 



The origin of the blood-globules after birth and in the adult still 

 remains one of the most obscure portions of their history, in spite 

 of the numerous endeavours which have been specially directed to 

 this point. The hypothesis which appears to me deserving of the 

 most confidence is that which considers the red blood-cells to arise 

 from the smaller chyle-corpuscles, which lose their nuclei and 

 become flattened, while haematine is produced in their interior. 

 These cells are not far from the same size as the blood-globules, 

 or are even somewhat smaller ; their membrane exhibits the same 

 structure, they are flattened, and are not unfrequently coloured 

 faintly yellow ; hence they may pass into coloured cells without 

 any considerable alteration, only such as we see in the colourless 

 blood-cells of the embryo. No one has yet observed where and 

 how the transformation takes place; and although I have devoted 

 much trouble and care to this subject, I have never seen a nu- 

 cleated, coloured blood-cell in the adult. The only observation 

 bearing on this point which I have to record is, that in the pul- 

 monary veins, and occasionally, also, in other blood, the smaller 

 lymph-corpuscles have frequently appeared with a really pretty 

 distinct colour, much more than in the thoracic duct ; and thus it 

 has happened that, as thev lay on their sides, thev were seareely 



