132 DEVELOPMENT OF THE BLOOD. 



The /preponderance of nucleated coloured corpuscles in the blood of 

 the very early mammalian embryo, and their gradual diminution in 

 quantity as the foetus increases in age was noticed by Kdlliker. In other 

 observations which the writer made with Mr. Paget on the blood of two 

 embryonic sheep, each about seven lines in length, the truth of this remark 

 was fully confirmed, as also of the fact observed by other physiologists that 

 the blood corpuscles of the foetus are decidedly larger than those of the 

 adult. In the blood of each of the embryonic sheep by far the majority of the 

 corpuscles were coloured, had a diameter at least twice as large as that of 

 the red corpuscles in the uterine vein of the parent, and were biconvex in 

 form, often somewhat distorted, and Saturn-shaped ; the addition of water 

 brought into view nuclei in almost all of them.* 



With regard to the development or fresh formation of corpuscles in the 

 blood after the cessation of embryonic life, Kolliker favours the view advo- 

 cated by the translator of Miiller's Physiology,! and adopted by many 

 physiologists, that this is effected by the transformation of the pale cor- 

 puscles of the blood, which (developed in the liver during embryonic life, 

 after this period) are identical with the corpuscles found in the lymph 

 and chyle. In this transformation the corpuscles possibly pass through 

 transitional stages somewhat similar to those undergone by the pale cor- 

 puscles of the embryonic blood, though, if this be so, the whole process 

 must take place most rapidly, for the occurrence of the stage of coloured 

 nucleated corpuscle is one of extreme rarity, and has never been observed 

 in the blood of the human subject. Mr. Wharton Jones states that he 

 has seen it in the blood of the horse, and of the elephant. Dr. Carpen- 

 ter,! however, and some other physiologists are still of opinion that the 

 red corpuscles do not owe their origin to the pale ones, but that they 

 multiply either by the division of each corpuscle into two, as maintained 

 by Dr. Owen Rees, or by its breaking up into six or more segments, 

 each of which becomes a young blood-disc, as described by Dr. Barry. || 



* Subsequent examinations of the blood of several embryonic sheep of various sizes with 

 the particulars of which the writer has been kindly furnished by Mr. Paget, would seem to 

 prove a constant resemblance, except in form, between the characters of Mammalian blood at 

 all periods of embryonic life before the disappearance of the branchial fissures, and those of the 

 blood of fish, in which animals the branchial apparatus is persistent. And it would appear 

 that those peculiarities which characterize the blood of Mammalian animals during extra- 

 uterine life are assumed by the foetus at the time of, or just after, the closure of the branchial 

 fissures. t Vol. i. page 155. 



Principles of Human Physiology, third edition, p. 107. 



Gulstonian Lectures, Medical Gazette, March, 1845. || Phil. Trans. 1840. 



FINIS. 



LONDON : Printed by S. & J. BENTLEY, WILSON, and FLEY, Banger House, Shoe Lane. 



