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 

 iavourably 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 Vertebrated 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. 



