œsophagus at work. No: the Rotifer once _dried_ is dead, and dead for ever. But if, like a cautious experimenter, you vary and control the experiment, and beside the glass-slide place a watch-glass containing Rotifers with dirt, or moss, you will find that the addition of water to the contents of the watch-glass will often (not always) revive the animals. What you cannot effect on a glass-slide without dirt, or with very little, you easily effect in a watch-glass with dirt, or moss; and if you give due attention you will find that in each case the result depends upon the quantity of the dirt. And this leads to a clear understanding of the whole mystery; this reconciles the conflicting statements. The reason why Rotifers ever revive is, because they have not been _dried_—they have not lost by evaporation that small quantity of water which forms _an integral constituent of their tissues_; and it is the presence of dirt, or moss, which prevents this complete evaporation. No one, I suppose, believes that the Rotifer actually revives after once being dead. If it has a power of remaining in a state of suspended animation, like that of a frozen frog, it can do so only on the condition that its _organism_ is not destroyed; and destroyed it would be, if the water 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.