60 OKGANISED FLUIDS. 



Oviparous Vertebrata are of a nature totally distinct from the 

 ordinary blood cells of the Mammalia, which have no nuclei, 

 but that the nuclei of the blood cells of the former are the 

 analogues of the latter; this opinion is scarcely consistent with 

 the difference of structure and chemical composition observed 

 between the two. Opinions very analogous to those of Mr. 

 Jones in reference to the nafure of the blood corpuscles of 

 the mammalia, viz. that they are escaped nuclei, appear to 

 have been entertained by Mr. Gulliver from observations 

 made on the horse; this gentleman supposing that the 

 red corpuscle was the escaped nucleus of the white granular 

 corpuscle, while Mr. Jones conceives that the red blood disc 

 is the liberated nucleus of the same body, only in an ad- 

 vanced condition of its development, in the stage of coloured 

 nucleated blood cell. 



To the appellations by which Mr. Jones designates two of 

 his phases of the development of the blood corpuscle an 

 exception may fairly be taken. The (f granule blood cell " 

 is frequently nucleated, even while it still retains its granular 

 structure, and therefore the term selected by Mr. Jones to 

 indicate a condition of the blood corpuscle distinct from its 

 granular state, viz. that of nucleated blood cell, is inappropri- 

 ate, and calculated to lead to the inference that the granule 

 blood cell is not a nucleated body. 



I reiterate then the opinion, that the white and red 

 globules of the blood are wholly distinct from each other, 

 distinct in origin, in structure, and in function. 



The strongest fact with which I am acquainted (but it is one 

 which is not employed by M. Donne), in favour of the trans- 

 mutation of white globules into red, is this, viz. that the 

 nucleus which exists in the blood discs of the frog, and rep- 

 tiles in general, is of a granular structure, in all respects 

 similar to that of a white globule, with the differences only 

 of size and form, the nucleus being four or five times smaller 

 than a true white globule, and of an oval instead of a circular 

 outline. (See Plate II. fig. 5.) One of these differences, as 

 already stated, viz. that of form, is effaced by water, which 

 renders the nucleus circular (see Plate II. fig. 4.), in which 



