1890-91.] AMPHIBIA BLOOD STUDIES. 255 



greenish elements of the cytoplasma in both being yolk spherules colored 

 by the reduction of the chromic acid. In the corpuscles at this stage 

 karyokinesis is not more common than it is in ordinary tissue cells. It 

 would appear that the more numerous class of corpuscles, i. e., those 

 reacting deeply with eosin, become converted into the mature blood cells 

 existing in the larva up to the twenty-fifth day, for it is these cells only 

 which illustrate the specialization of form and structure already described 

 and partly represented by Figs. 19-21. The cells which react with 

 haematoxylin alone constitute the persistent elements which ultimately 

 become the frequently dividing haematoblasts of the later stages of de- 

 velopment. The eosinophilous cells are apparently in a condition of 

 degeneration, for the division of their nuclei is not always followed by a 

 division of the cell (Fig. 18). Both classes of haematoblasts at this time 

 do not specially illustrate division but those which stain with haema- 

 toxylin only seem to retain the capacity for proliferation while the 

 eosinophilous elements gradually lose it within the next ten days. 



At a period which seems to coincide with the formation of the liver as 

 a vascular organ and with the development of tubules in it, the haemato- 

 blasts, which, from the sixteenth to the nineteenth day, when hardened in 

 chromic acid, stain with haematoxylin only, now begin to acquire a capa- 

 city for proliferation far in excess of that which they previously had. It 

 would appear that this change is associated with the appearance, in the 

 blood vessels of the body generally and of the liver specially, of a serum 

 which stains very deeply with eosin. This serum stains slightly with 

 alum-cochineal but greenish-blue or green, like the yolk spherules, with 

 the Indigo-carmine Fluid described in the foregoing pages. I regard this 

 staining capacity of the serum as due to the solution of yolk or rather of 

 that constituent of it which has been called haematogen by Bunge. This 

 is but a reserve form of chromatin and as the undifferentiated haema- 

 toblasts float in the serum, it is reasonable to believe that they absorb the 

 dissolved chromatin. It is from this time on that the haematoblasts begin 

 to manifest the incessant divisions which characterize the stage repre- 

 sented by Figs. 9, 10 and ii. It is at this time also that the chromatic 

 figures of the haematoblasts increase in size. Previously their figures were 

 not larger than those of the other cells of the body. These facts can be 

 explained in no other way than by assuming that the haematoblasts sur- 

 viving as such, absorb the chromatin or " heematogen " which is dissolved 

 in the serum and thereby entered on a phase of renewed vitality. The 

 other cells in the body also exhibit divisions now more frequently than 

 before this stage, though not by any means as frequently as the haemato- 

 blasts, and this increased capacity for proliferation may also be explained 



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