166 OP THE BLOOD. 



rudiment of the heart, that this metamorphosis seems first to take place. The 

 situation of the heart, and the course of the principal trunks of the "vascular 

 area," are early marked out by the peculiar disposition of the aggregations of 

 cells from which these organs are to be developed ; and whilst the outer portions 

 of these aggregations are transformed into the walls of the respective cavities, 

 the inner portions seem partly to deliquesce, and partly to remain as isolated 

 cells floating in the liquid thus produced. These isolated cells are the first 

 blood-corpuscles ; and the following account of them is given by Mr. Paget, 1 

 who has made them the subject of careful study. " As described by Vogt, 

 Kolliker, and Cramer, they are large colorless vesicular spherical cells, full of 

 yellowish particles of a substance like fatty matter (Fig. 14, A) j many of which 

 particles are quadrangular and flattened, and have been called stearine-plates, 



Fig. 14. 



Development of the first set of red corpuscles in the blood of the Batrachian larva. A. An embryo-cell, filled 

 with fatty-looking particles. B, c, D, and E. Successive stages in the transition of the embryo-cell to a blood- 

 corpuscle, as described in the text. F. A fully-formed blood-corpuscle. 



though they are not proved to consist of that or any other unmixed fatty sub- 

 stance. Among these particles each cell has a central nucleus, which, however, 

 is at first much obscured by them. The development of these embryo-cells into 

 the complete form of the corpuscles is effected by the gradual clearing-up, as if 

 by division and liquefaction, of the contained particles, the acquirement of blood- 

 color and of the elliptical form, the flattening of the cell, and the more promi- 

 nent appearance of the nucleus/' The process appears to be essentially the 

 same in the Fish, the Reptile, and the Bird ; but it takes place too rapidly in 

 the latter class for its stages to be clearly distinguished ; whilst in the tadpole 

 the changes occur so slowly that they can be traced in the blood even while it 

 circulates. The history of the development of the first red corpuscles in Mam- 

 malia is nearly the same ; but a binary multiplication of these bodies by sub- 

 division has been observed in them, which has not been noticed elsewhere (Fig. 

 15, A, D). In watching the stages of this process, it is seen that the partition 

 of the nucleus takes place completely, before that of the cell itself has com- 

 menced. The blood-corpuscles of the Human embryo thus formed, are de- 

 scribed by Mr. Paget as " circular, thickly disk-shaped, full-colored, and, on an 

 average, about ^ -2500th of an inch, in diameter; their nuclei, which are about 

 l-5000th of an inch in diameter, are central, circular, very little prominent 

 on the surfaces of the cell, and apparently slightly granular or tuberculated. 

 In a few instances, cells are found with two nuclei ; and such cells are usually 

 large and elliptical, with one of the nuclei near each end of the long axis." 



1 This account is cited from Messrs. Kirkes and Paget's "Manual of Physiology," (pp. 

 62-6, Am. Ed.,] in which it appears as an abstract of a part of Mr. Paget's Lectures on 

 the " Life of the Blood," delivered at the College of Surgeons in 1848. 



