BLOOD-CORPUSCLES. G9 



never distinctly observed nucleoli in it ; occasionally only 

 I thought I perceived something of the kind, for instance, in 

 the blood-corpuscles of a salamander j it was not, however, snf- 

 ciently evident to permit of my asserting their presence. Cell- 

 contents must certainly exist ; for if the cell-walls lay imme- 

 diately upon one another, the corpuscle must be as much 

 thinner on the margins beside the nucleus as the thickness of 

 . the nucleus amounts to. If it be assumed that the cell-mem- 

 brane alongside the nucleus may be so much thicker as thereby 

 to produce the almost level side surfaces, the cell- membrane 

 must in such case have a thickness equal to the half of that 

 of the corpuscle ; but it would then be sufficiently thick to 

 allow of a double outline being distinguished when it was 

 swollen by water ; observation, however, does not detect any 

 such appearance. The red colouring matter forms the cell- 

 contents. It is difficult to decide whether the cell-membrane 

 and nucleus are also coloured, but it is in some degree pro- 

 bable that they are so, since otherwise the centre of the 

 corpuscle where the nucleus lies must appear white, whilst it 

 in fact exhibits a paler red colour. The colouring matter of 

 the blood-cells is not contained in granules, as it is in most 

 kinds of pigment, but in a state of solution. If the lymph- 

 corpuscles be cells, their transformation into the blood-corpus- 

 cles may at least be conjectured as taking place by their 

 becoming flattened and absorbing colouring matter. Those 

 blood-corpuscles in which the envelope (hiille) is smaller in 

 proportion to the nucleus, a fact often observed in the frog, 

 arc probably younger cells. I have made no observations 

 upon the formation of the blood-corpuscles in the germinal 

 membrane. According to C. II. Schultz (System dcr Cir- 

 kulation, p. 33), the blood- corpuscles in the chick are formed 

 round the yelk-globules. (?) The latter are first present, and 

 form the nucleus of the blood-corpuscles ; they become sur- 

 rounded with a delicate membrane. The vesicle then dilates, 

 and at length becomes flattened. This description accords 

 excellently with the fundamental laws previously developed, 

 and shows that as early as 183G Schultz had discovered the 

 pre-existence of the nucleus of the blood-corpuscle, the for- 

 mation of the blood- vesicle around it, and the gradual expansion 

 of that vesicle. 



