BLOOD-CORPUSCLES. 69 
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 ; it was not, however, suf- 
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 m 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, 
are probably younger cells. I have made no observations 
upon the formation of the blood-corpuscles in the germinal 
membrane. According to C. H. Schultz (System der 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 1836 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. 
