THE BLOOD. 61 



state the only distinction between it and a white corpuscle 

 which can be detected is the single one of size. (See Plate 

 II. Jiff. I.) This difference, however, is so great, and coupled 

 with the fact that no white globules have ever been detected 

 in the frog, putting on the characters of a true red blood cor- 

 puscle, that the opinion that the white globules are trans- 

 formed into red blood discs must again be abandoned. The 

 existence of a granular nucleus in the blood discs of reptiles, 

 &c. revives again the old notion, that the white globules are 

 the escaped nuclei ; that they are not so is proved by the 

 fact that no such nuclei exist in the true blood globules of 

 man and the mammalia, in the blood of which white cor- 

 puscles abound.* The blood discs, it has been observed, 

 first make their appearance in the chyle : any inquiries, there- 

 fore, instituted with the view of determining their origin and 

 development in man, would be more likely to prove successful 

 if directed to the rigorous examination of that fluid, f 



In the last place, it remains to treat of the end or final 

 destination of the red globules of the blood. 



* The following interesting remarks of Mr. Gulliver tend to confirm 

 somewhat the views of M. Donne : they are by no means conclusive 

 however : " White globules about the same size as those in the blood of 

 man, and probably identical with the proper globules of chyle and lymph, 

 are common in the blood of birds, and particularly abundant after a full 

 meal in the vultures and other rapacious families. Some of the red discs, 

 too, instead of the oval form, are often nearly or quite circular in figure. 

 Hence the blood of these birds would appear especially favourable to ob- 

 serve any changes in the white globules ; and it seemed highly probable, 

 that these might be transformed into the blood discs in the manner men- 

 tioned by Dr. Baly ; but although I made many observations with the 

 view of determining this question, nothing but negative results were 

 obtained." (Appendix to Gerbers General Anatomy, p. 24.) This ob- 

 servation is satisfactory in one respect, viz. that it shows clearly the 

 connection, which has already been dwelt upon, of the white corpuscles 

 with nutrition. 



f For further observations on the development of the red blood disc, 

 see the remarks on the circulation in the embryo of the fowl. 



i- 4 



