were removed from its tissues: for, strange as it may seem, water is not an accessory, but a constituent element of every tissue; and this cannot be replaced mechanically—it can only be replaced by vital processes. Every one who has made microscopic preparations must be aware that when once a tissue is desiccated, it is spoiled: it will not recover its form and properties on the application of water; because the water was not originally worked into the web by a mere process of imbibition—like water in a sponge—but by a molecular process of assimilation, like albumen in a muscle. Therefore, I say, that desiccation is necessarily death; and the Rotifer which revives cannot have been desiccated. This being granted, we have only to ask, What prevents the Rotifer from becoming completely dried? Experiment shows that it is the presence of dirt, or moss, which does this. The whole marvel of the Rotifer's resuscitation, therefore, amounts to this:—that if the water in which it lives be evaporated, the animal passes into a state of suspended animation, and remains so, as long as its own water is protected from evaporation.
I am aware that this is not easily to be reconciled with M. Doyère's experiments, since the application of a temperature so high as 300° Fahr. (nearly a hundred degrees above boiling water) must, one would imagine, have completely desiccated the animals, in spite of any amount of protecting dirt. It is possible that M. Doyère may have mistaken that previously-noted swelling-up of the bodies, on the application of water, for a return to vital activity. If not, I am at a loss to explain the contradiction; for certainly in my experience a much more moderate desiccation—namely, that obtained by simple evaporation over a mantelpiece, or under a large bell-glass—always destroyed the animals, if little or no dirt were present.
The subject has recently been brought before the French Academy of Sciences by M. Davaine, whose experiments[1] lead him to the conclusion that those Rotifers which habitually live in ponds will not revive after desiccation: whereas those which live in moss always do so. I believe the explanation to be this: the Rotifers living in ponds are dried without any protecting dirt, or moss, and that is the reason they do not revive.
After having satisfied myself on this point, I did what perhaps would have saved me some trouble if thought of before. I took down Spallanzani, and read his account of his celebrated experiments. To my surprise and satisfaction, it appeared that he had accurately observed the same facts, but curiously missed their real significance. Nothing can be plainer than the following passage: "But there is one condition indispensable to the resurrection of wheel-animals: it is absolutely necessary that there should be a certain quantity of sand; without it they will not revive. One day I had two wheel-animals traversing a drop of water about to evaporate, which contained very little sand. Three quarters of an hour after evaporation, they were dry and motionless. I moistened them with water to
- ↑ Davaine in Annales des Sciences Naturelles, 1858, x. p. 335.
