A proteid, in the same way, is a chemical combination of the elements already mentioned—carbon, oxygen, hydrogen, nitrogen, and sulphur—but the proportions by volume of these elements to each other are represented by very high figures, not merely by two to one, as in the case of water. It is the carbon in them that makes “proteids” turn black when they are destroyed by burning, and it is the sulphur which causes the smell of rotten eggs. Whilst an ultimate molecule or physical particle of water consists of two atoms of hydrogen and one of oxygen—the molecule of the proteid called “albumen” is built up by seventy-two atoms of carbon, one hundred and twelve atoms of hydrogen, eighteen atoms of nitrogen, twelve atoms of oxygen, all brought into relation with one atom of sulphur. Probably in some other proteids the number of these atoms must all be multiplied by three. The elaborate “atomic composition” of a molecule of proteid renders it very unstable; it easily falls to pieces, the elements combining, in other and simpler proportions, to form less “delicate” bodies. Living protoplasm consists chiefly of proteids and of compounds which are on the way up, forming step by step more elaborate combinations till they reach the proteid stage—and of many others which are degradation products, coming down, as it were, from the giddy heights of the proteid combination. The protoplasm of a cell contains finer and grosser granules, which are these ascending and descending substances; it also contains others in solution and invisible—for, like a lump of jelly (such as the cook serves up shaped by a mould and soaked with flavour and colour), protoplasm can soak up either a large or a small quantity of water, and with the water (that is the important point) all sorts of chemical bodies soluble in water. Just as a lump of quivering calves’-foot jelly (which is a chemical compound of a lower grade than proteids, but like them), when placed in a shallow dish of water coloured red by carmine, does not dissolve in the water, but absorbs the water and the carmine, allowing the coloured water and any chemical bodies in solution in it to diffuse into and become physically, though not chemically, a part of its substance, so protoplasm takes up water and the compounds dissolved by it. Just as a “jelly” of water-holding gelatine can give up its water and become hard and horny, so is protoplasm capable of gradually giving up much of its water, and even in some cases of becoming hard and horny, yet able to return, when remoistened, to its active state. Moreover, a “jelly” can be made to “soak up” or take into itself water and let it pass through its substance, so as to wash out from it all soluble matters. In the same way the protoplasm of a living cell is supplied with nourishing and oxygenating fluids which diffuse into it, and is “washed out,” purified, and cleansed of waste or effete chemical compounds by the water which first permeates it, and then diffuses out