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 generations have been sufficiently numerous to spread the species throughout a great part of Europe. M. Hoogewerf showed a great flask full to the Dutch biologists who met at Utrecht in 1891. M. L. Errera presented others in June 1899, to the Society of Medical and Natural Sciences at Brussels. To-day the great manufactory of Sarg & Co., of Vienna, is engaged in their production on a large scale for industrial purposes.

Thus we are able to study this crystalline species of glycerine and to determine with precision the conditions of its continued existence. It has been shown that it does not resist a temperature of 18°, so that if precautions were not taken to preserve it, a single summer would suffice to annihilate all the crystalline individuals existing on the surface of the globe, and thus the species would be extinguished.

Possible Extinction of a Crystalline Species.—As these crystals melt at 18°, this temperature represents the point of fusion of solid glycerine or the point of solidification of liquid glycerine. But the liquor does not solidify at all if its temperature falls below 18° C., as we well know, for it is at that temperature we use it. Nor does it solidify at zero, nor even at 18° below zero; at 20°, for instance, it merely thickens and becomes pasty. We only know glycerine, then, in a state of superfusion, a fact which chemists have not learned without amazement. Under these conditions, so analogous to the appearance of a living species, to its unlimited propagation and to its extinction, the mineral world offers a quite faithful counterpart to the animal world. The living body illustrates here the history of the brute body and facilitates its exposition. Inversely, the brute body in its turn