ISOLATED CELLS OF ANIMAL FLUIDS. 
45 
inquiries, that the blastema will resolve itself into fibres or 
into cells, according as the wound is completely secluded from 
the air, or is exposed to it. It is under the former condition 
that losses of substance are most rapidly and most completely 
repaired; whilst it is under the latter that inflammation is 
most likely to arise, in consequence of the bad effect pro¬ 
duced by the contact of air with the raw surface; the 
process of healing, when thus interfered with, going on less 
favourably as well as more slowly. 
35. The very simplest and most independent condition of 
the animal Cell, is probably to be found in the nutritive fluids 
of the body; in which we meet with floating cells that are 
completely isolated from each other, and which are conse¬ 
quently just as self-sustaining as are the separate vesicles of 
the Yeast-plant, of the Eed Snow, or of other simple cellular 
Plants. These cells are of two classes. In the blood of 
animals generally, and in the chyle and lymph of Yertebrata, 
we find a larger or smaller proportion of colourless corpuscles, 
which are usually nearly spherical in form, and which exhibit 
various stages of development into cells, being sometimes 
little else than collections of granules, without any distinct 
enveloping membrane, whilst, in other instances, there is a 
distinct cell-wall, cell-cavity, and nucleus. These bodies, if 
watched under a sufficiently powerful microscope, may often 
be seen to undergo very curious changes of form, resembling 
those of the Amoeba (§ 129). Besides the foregoing, however, 
the blood of Yertebrated animals contains a far larger pro¬ 
portion of red corpuscles, which are flattened disks, sometimes 
circular but more commonly oval, having pellucid and colour¬ 
less walls, but having their cavities filled with a peculiar 
coloured fluid. As these will be more fully described here¬ 
after (§ 229), it is not requisite to do more than notice them 
here as constituting a most important part of the animal 
organism, probably not less than a twelfth part of the entire 
weight of Man and the higher animals, being thus composed 
of nothing else than these isolated cells. 1 
36. Next in independence to the cells or corpuscles float¬ 
ing in the animal fluids, are those which cover the free 
1 The entire weight of the blood of Man seems to be about one-sixth 
part of that of the body; and the moist corpuscles constitute about half 
the entire weight of the blood. 
