ITS PHYSICAL, CHEMICAL, AND STRUCTURAL CHARACTERS. 167 



This first brood of red corpuscles soon disappears, when the lymph and chyle 

 begin to be poured into the blood, being superseded by those developed from the 

 corpuscles brought in by them ; and this epoch generally corresponds closely 

 with the alteration in the embryonic circulation, which consists in the oblite- 



Fig. 15. 



Development of the first set of red corpuscles in the Wood of the Mammalian emhryo. A. A dotted, nu- 

 cleated embryo-cell, in process of conversion into a blood-corpuscle : the nucleus, provided with a nucleolus. 

 B. A similar cell with a dividing nucleus; at c, the division of the nucleus is complete; at D, the cell also is 

 dividing. E. A blood-corpuscle almost complete, but still containing a few granules, r. Perfect blood-cor- 

 puscles. 



ration of the branchial arches (CHAP. xix.). In the Human embryo, the first 

 set of corpuscles seems to disappear entirely by the end of the second month, 

 except in cases of arrested development. 



150. The doctrine that the continued generation of Red corpuscles is due to 

 the metamorphosis of the Chyle- and Lymph-corpuscles, the Colorless corpuscles 

 of the Blood constituting an intermediate stage of development, is one which 

 has come of late to be very generally received amongst Physiologists ; it may 

 be found, however, to require some modification. It rests upon facts of three 

 different orders : 1st, the presence, in all ordinary Blood,"of corpuscles exhi- 

 biting what appear to be intermediate gradations of development between the 

 Lymph-corpuscle and the true Red corpuscle ; and this especially in blood in 

 which an unusually rapid development of red corpuscles is taking place, to make 

 up for previous loss ; 2d, frequent ruddiness in the hue of the fluid of the Tho- 

 racic duct, which seems to depend upon the incipient development of Haematine 

 in some of its floating corpuscles ; and 3d, the progressive transition from one 

 form to the other, which may be observed in the ascending scale of animal 

 existence. To these considerations may be added, the absence of any other 

 mode of production that can be suggested ; since the idea of the self-multiplica- 

 tion of the Red corpuscles is almost certainly erroneous, and no special organ 

 can be assigned as the seat of their generation. 1 The transition-stages between 



1 According to the observations of Weber ("Henle and Pfeufer's Zeitschrift," 1846, 

 and "Canstatt's Jahresbericht," 1848), the Liver of oviparous animals appears to assist 

 in the production of the Red corpuscles, from the materials furnished by the yolk, during 

 the latter part of intra-oval life, in the Frog and in the Chick. In the Mammal, however, 

 the contents of the yolk-bag (or umbilical vesicle) are exhausted at a very early period of 

 embryonic life, when as yet the liver is rudimentary ; so that if this organ takes any share 

 in the development of red corpuscles, it can only perform such a function for a very brief 

 time. At no subsequent period is there any evidence that the Liver is concerned in the 

 development of Red corpuscles; and although the Spleen has been supposed to act as their 

 matrix, yet all the evidence at present in our possession shows that neither to this nor to 

 , any other of the "vascular glands" can such a function be justly assigned (g 172). 



