68 



BLOOD-CORPUSCLES. 



the blood-corpuscles to be vesicles. 1 He relied especially upon 

 the manner in which they were acted on by water, whereby 

 they lose their colouring matter, swell, and become round, and 

 under which circumstances he frequently saw the nucleus roll 

 about within the round and very transparent vesicle. The last 

 fact would of itself be sufficiently conclusive. I have not as 

 yet observed this fact ; on the contrary, in most instances, the 

 nucleus decidedly adheres to the internal surface of the wall 

 of the vesicle, eccentrical as in all cells, though it may pro- 

 bably also sometimes become detached. The fact, however, of 

 the blood-corpuscles becoming swollen and round, renders their 

 cellular nature highly probable. If the envelope (hiille) of the 

 blood-corpuscle were not a flattened vesicle, it might indeed 

 lose its colour and swell in water, but it would retain its flat 

 form, like a sponge when filling with fluid. The circumstance 

 of the nucleus remaining on the wall during the swelling of 

 the blood-corpuscle in water is no accidental appearance; for 

 even in the round blood-corpuscles of a chick, forty-eight 

 hours after the commencement of incubation, when they were 

 not as yet flattened, I found that the nuclei, which were also 

 circular, were not placed in the centre, but lay eccentrical upon 

 the internal surface of the wall. The cellular nature of the 

 blood-corpuscle, and the signification of its separate parts 

 scarcely appear to admit of doubt when regarded in connexion 

 with the whole of this investigation. It is a flattened cell fur- 

 nished with a cell-nucleus, which is fixed to a spot on the in- 

 ternal surface of the cell-membrane. The size of the cell as 

 compared with the nucleus is not the same in all corpuscles ; 

 that of the nucleus is much more constant. The nucleus of 

 some blood-corpuscles of frogs which had swollen in water, also 

 appeared to me in some instances to be hollow. It also loses 

 its flatness in water, but retains its oval figure. I have 



1 [This is clearly an oversight as Hewson not only demonstrated their vesicular 

 nature, and called them vesicles, but accurately described their becoming " changed 

 from a flat to a spherical shape," on the addition of water to the blood, and the falling 

 of the nucleus " from side to side in the hollow vesicle, like a pea in a bladder." See 

 'Philosophical Transactions,' 1773, vol. lxiii, Part II ; or, 'Experimental Inquiries,' 

 Part III, being ' a Description of the Red Particles of the Blood,' &c.,&c. (published 

 after his death), edited by Magnus Falconar, London, 1777 ; also the very valuable 

 republication of Hewson's Works by the Sydenham Society, edited by George Gulliver, 

 Esq., where the reader is particularly referred to pp. 220, 221. — Trans.] 



