PHYSIOLOGICAL LIGHT. 415 



the Photobacterium sarcophilum, the Photobacteriacece are not luminous 

 in acid gelatin peptone. That bacterium, however, does not really form 

 an exception to the common law, but it possesses the property of secret- 

 ing an alkaline substance which, by neutralizing the acid medium, per- 

 mits the photogenic function to operate. It therefore creates for itself 

 a medium where others would succumb to the influence of the environ- 

 ment. 



The luminosity quite frequently seen in autumn in the forests on dead 

 leaves or on fragments of young or old wood, and even in mines on 

 worm-eaten beams, is often, if not always, due to the vegetative organs 

 of mushrooms of quite high organization, especially certain Hymeno- 

 mycetes, the Agaricus melleus, for example, whose slender filaments 

 penetrate the ligneous tissues, forming an easily recognized, whitish 

 network. These luminous myceliums have even been successfully cul- 

 tivated. Still, I have vainly sought them on pieces of very young wood, 

 freshly broken, that presented over their entire surfaces a steady and 

 regular phosphorescence that in certain cases might indeed be a 

 result of a necrobiotic alteration of the tissues or the work of microbic 

 parasites. But the microbes found on these fragments have not pro- 

 duced luminous cultures, neither have those which live in symbiosis on 

 the higher photogenic mushrooms. 



In certain mushrooms at an adult age the photogenic function is 

 well marked. The laminas of the Agaricus olearius, which is quite 

 common in Provence at the foot of olive trees, gives out a bluish light 

 that follows the fluctuations of vitality in the mushroom. It does not 

 reside in any specially differentiated part, but only where the spores 

 are developed. 



Luminous exotic mushrooms are quite numerous. There is known 

 in Brazil the Agaricus Gardneri, in Australia the Agaricus phosphoreus, 

 candescens, lampas, illuminans, etc., whose names indicate their singu- 

 lar property. Some of them give enough light to make it possible to 

 read by means of this living torch. 



It can not be affirmed that in the vegetables we have mentioned the 

 light is the result of a secretion. It seems rather to have its origin in 

 the protoplasm, for when a bouillon made luminous by Photobacteria is 

 filtered through a porcelain tube it loses its light; it would be other- 

 wise if the photogenic substance were really dissolved in the ambient 

 liquid. 



II. 



The photogenic function is likewise widely found among very inferior 

 animals, the Noctiluca miliaris, for example, to which is often due the 

 splendid phenomena of ocean phosphorescence. Besides its envelope, 

 some intercellular liquid, its digestive vesicles, and a flagellum, the 

 structure of the Noctiluca is that of an active, contractile, protoplas- 

 mic mass, surrounding a nucleus and sending toward the internal wall 



