startling to me, because I had myself often witnessed the reawakening of these dried animals. Nevertheless, whenever a doubt is fairly started, we have not done justice to it until we have brought it to the test of experiment; accordingly I tested this, and quickly came upon what seems to me the source of the general misconception. Day after day experiments were repeated, varied, and controlled, and with results so unvarying that hesitation vanished; and as some of these experiments are of extreme simplicity, you may verify what I say with little trouble. Squeeze a drop from the moss, taking care that there is scarcely any dirt in it; and, having ascertained that it contains Rotifers, or Tardigrades,[1] alive and moving, place the glass-slide under a bell-glass, to shield it from currents of air, and there allow the water to evaporate slowly, but completely, by means of chloride of calcium, or sulphuric acid, placed under the bell-glass; or, what is still simpler, place a slide with the live animals on the mantelpiece when a fire is burning in the grate. If on the day following you examine this perfectly dry glass, you will see the contracted bodies of the Rotifers, presenting the aspect of yellowish oval bodies; but attempt to resuscitate them by the addition of a little fresh water, and you will find that they do not revive, as they revived when dried in the moss: they sometimes swell a little, and elongate themselves, and you imagine this is a commencement of resuscitation; but continue watching for two or three days, and you will find it goes no further. Never do these oval bodies become active crawling Rotifers; never do they expand their wheels, and set the 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
- ↑ The Tardigrade, or microscopic Sloth, belongs to the order of Arachnida, and is occasionally found in moss, stagnant ponds, &c. I have only met with four specimens in all my investigations, and they were all found in moss. Spallanzani described and figured it (very badly), and M. Doyère has given a fuller description in the Annales des Sciences, 2nd series, vols. xiv. xvii. and xviii.
