_F._ A white corpuscle magnified same as _B._; _G._ ditto, throwing out some blunt processes; _K._ ditto, treated with acetic acid, and showing nucleus, magnified same as _D._ _H._ Red corpuscles puckered or crenate all over. _I._ Ditto, at the edge only. ] =round bodies, the blood discs or blood corpuscles= (Fig. 4, _A_). If you look carefully you will notice that most of them are round, as _B_; but every now and then you see something like _C_. That is one of the round ones seen sideways; for they are not round or spherical like a ball, but circular and dimpled in the middle, something like certain kinds of biscuit. When you see one by itself it looks a little yellow in colour, that is all; but when you see them in a lump, the lump is clearly red. Remember how small they are: three thousand of them put flat in a line, edge to edge, like a row of draughts, would just about stretch across one inch. All the redness there is in blood belongs to them. When you see one of them, you see so little of the redness that it seems yellow. If you were to put a drop of blood into a tumbler of water, the water would not be stained red, but only just turned of a yellowish tint, so little redness would be given to it by the drop of blood. In the same way a very very thin slice of currant jelly would look yellowish, not red. These red corpuscles are not hard solid things, but delicate and soft, very tender, very easily broken to pieces, more like the tiniest lumps of red jelly than anything else, and yet made so as to bear all the squeezing which they get as they are driven round and round the body. Besides these red corpuscles, you may see if you look attentively =other little bodies, just a little bigger than the red corpuscles, not coloured at all, and not circular and flat, but quite round like a ball= (Fig. 4, _a_, _F_, _G_). That is to say, these are very often quite round, only they have a curious trick of changing their form. Imagine you were looking at a suet dumpling so small that about two thousand five hundred of them could be placed side by side in the length of one inch--and suppose the round dumpling while you were looking at it gradually changed into the shape of a three-cornered tart, and then into a rounded square, and then into the shape of a pear, and then into a thing that had no shape at all, and then back again into a round ball, and kept doing this apparently all of its own accord while you were looking at it--wouldn’t you think it very curious? Well, one of these little bodies in the blood of which we are speaking, and which are called white corpuscles, may be seen, when a drop of blood is watched under the microscope, to go on in this way, continually changing its shape. But of these =white corpuscles= of the blood, and of their wonderful movements, you will learn more as you go on in your physiological studies.