- [Footnote: atmosphere that the light-evolving animalculæ come in large
numbers to the surface of the sea. It has been asked why the fresh water of our marshes, which is filled with polypi, is never seen to become luminous. Both in animals and plants, a particular mixture of organic particles appears to be required in order to favour the production of light. Willow-wood is oftener found to be luminous than oak-wood. In England experiments have succeeded in making saltwater shine by pouring into it the liquor from pickled herrings. It is easy to shew by galvanic experiments that in living animals the evolution of light depends on an irritation of the nerves. I have seen an Elater noctilucus which was dying emit strong flashes of light when I touched the ganglion of his fore leg with zinc and silver. Medusæ sometimes shew increased brightness at the moment of completing the galvanic circuit. (Humboldt, Relat. Hist. T. i. p. 79 and 533.)
Respecting the wonderful development of mass and power of increase in Infusoria, see Ehrenberg, Infus. S. xiii. 291 and 512. He observes that "the galaxy of the minutest organisms passes through the genera of Vibrio and Bacterium and that of Monas, (in the latter they are often only 1/3000 of a line,) S. xix. and 244.]*
