THE BLOOD. 59 



this appellation expresses the usual condition in which the 

 blood disc in the mammalia is encountered, and in which no 

 nucleus can be discovered. 



This third phase Mr. Jones considers to be derived from the 

 nucleated blood cell in its second stage ; the " free coeliform 

 nucleus" being the escaped nucleus of the nucleated blood cell. 



The facts by which this view is supported are, first, a 

 relation in size between the nucleus of the nucleated blood 

 cell and the ordinary blood disc, or " free coeliform nucleus," 

 and second, the occurrence, which is, however, very rare, of 

 nucleated cells from which the nuclei themselves have escaped. 



The "nucleated bltfod cell" Mr. Jones found abundantly 

 in the blood of an embryo ox, an inch and a quarter long; 

 very sparingly in that of the elephant and horse, and not at 

 all in the blood of the human subject: he encountered them, 

 however, freely in the chyle of man. 



Such is a brief statement of the views of Mr. Jones in 

 reference to the blood corpuscle, and of the chief facts by 

 which those views are supported : without taking upon my- 

 self to pronounce upon them decidedly, I yet must confess 

 that they carry with them but little conviction to my mind, 

 and that the facts adduced to sustain them are open to 

 considerable discussion. 



If the blood corpuscles of animals in general, and of the 

 mammalia in particular, pass through the successive phases 

 and stages described by Mr. Jones, how happens it, I would 

 ask, that in the blood of mammalia, and especially in that 

 of man, while we meet with so abundantly the first stage 

 of the first phase, that of granule blood corpuscle, viz. the 

 coarsely granular stage, and also the last phase indicated by 

 Mr. Jones, that of free coeliform nucleus, we do not fre- 

 quently encounter the intermediate stages and phase, 

 through which, according to Mr. Jones, the blood corpuscles 

 pass? To this question I do not think it easy to give a 

 satisfactory reply, consistent with the opinions of Mr. Jones. 

 The explanation which I would give of the absence of these 

 transition forms is, that they have no real existence. 



According to Mr. Jones the nucleated blood cells of the 



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