revive them; but in vain, notwithstanding that they were immersed in water many hours. Their members swelled to thrice the original size, but they remained motionless. To ascertain whether the fact was accidental, I spread a portion of sand, containing animals, on a glass slide, and waited till it became dry in order to wet it anew. The sand was carelessly scattered on the glass, so as to be a thin covering on some parts, and on others in a very small quantity: here the animals did not revive: but all that were in those parts with abundance of sand revived."[1] He further says that if sand be spread out in considerable quantities in some places, much less in others, and very little in the rest, on moistening it the revived animals will be numerous in the first, less numerous in the second, and none at all in the third.
It is not a little remarkable that observations so precise as these should have for many years passed unregarded, and not led to the true explanation of the mystery. Perhaps an inherent love of the marvellous made men greedily accept the idea of resuscitation, and indisposed them to attempt an explanation of it. Spallanzani's own attempt is certainly not felicitous. He supposes that the dust prevents the lacerating influence of the air from irritating and injuring the animals. And this explanation is accepted by his Translator.
[Since the foregoing remarks were in type, M. Gavarret has published (Annales des Sciences Naturelles, 1859, xi. p. 315) the account of his experiments on Rotifers and Tardigrades, in which he found that after subjecting the moss to a desiccation the most complete according to our present means, the animals revived after twenty-four hours' immersion of the moss in water. This result seems flatly to contradict the result I arrived at; but only seems to contradict it, for in my experiments the animals, not the moss, were subjected to desiccation. Nevertheless, I confess that my confidence was shaken by experiments so precise, and performed by so distinguished an investigator, and I once more resumed the experiments, feeling persuaded that the detection of the fallacy, wherever it might be, would be well worth the trouble. The results of these controlling experiments are all I can find room for here:—Whenever the animals were completely separated from the dirt, they perished; in two cases there was a very little dirt—a mere film, so to speak—in the watch-*glass, and glass-cell, and this, slight as it was, sufficed to protect two out of eight, and three out of ten Rotifers, which revived on the second day; the others did not revive even on the third day after their immersion. In one instance, a thin covering-glass was placed over the water on the slide, and the evaporation of the water seemed complete, yet this glass-*cover sufficed to protect a Rotifer, which revived in three hours.
If we compare these results with those obtained by M. Davaine, we can scarcely avoid the conclusion that it is only when the desiccation of
- ↑ Spallanzani: Tracts on the Natural History of Animals and Vegetables: Translated by Dalyell, ii. p. 129,
