Two experiments, both performed very early in the history of Bioluminescence, are of great importance in understanding the nature of animal light. Boyle (1667), as already mentioned, proved the necessity of air for the luminescence of wood and fish and Spallanzani (1794) showed that parts of luminous medusæ gave no light when dried but if moistened again would emit light as before. We see then, that air (oxygen), water, and some photogenic substance are necessary for the light production. Spallanzani's experiment, which has been confirmed for a great many luminous forms, shows also that animal luminescence is not a _vital_ process, in the same sense that the conduction of a nerve impulse is a vital process. A nerve loses its characteristic property of conduction on drying or maceration while luminous cells still possess the power to luminesce after drying or maceration. Using the terminology of the older physiology we may say that "living protoplasm" is not necessary for light production. The experiments of Boyle (1626-91) are of great interest, especially those in which he studied the behavior of shining wood under the receiver of his air pump. On October 29, 1667, he wrote: "Exp. I.: Having procured a Piece of _shining Wood_, about the bigness of a groat or less, that gave a vivid Light, (for _rotten Wood_) we put it into a middle sized _Receiver_, so as it was kept from touching the Cement; and the _Pump_ being set a-work, we observed not, during the 5 or 6 first Exsuctions of the Air, that the splendor of the included Wood was manifestly lessened (though it was never at all increased;) but about the 7th Suck, it seemed to glow a little more dim, and afterwards answered our Expectation, by losing of its Light more and more, as the Air was still farther pumped out; till at length about the 10th Exsuction, (though by the removal of the Candles out of the Room, and by black Cloaths and Hats we made the place as dark as we could, yet) we could not perceive any light at all to proceed from the _Wood_. "Exp. II.: Wherefore we let in the outward Air by Degrees and had the pleasure to see the seemingly extinguished Light revive so fast and perfectly, that it looked to us almost like a little Flash of Lightning, and the Splendor of the Wood seemed rather greater than at all less, than before it was put into the Receiver."