ON SOME PHYSICAL MANIFESTATIONS OF LIFE 67 



drew the conclusion that phosphorescent matter is irritable, and "irrita- 

 bility" is considered a sign of life. We must not, however, overlook 

 the possibility that stimulation of an animal may produce the process 

 of phosphorescence indirectly, e.g. by causing motions on the part of 

 the animal which bring the phosphorescent matter into contact with 

 oxygen. Giesebrecht* has furnished an absolute proof for the fact 

 that phosphorescence may be produced in animals by non-living mate- 

 rial. He found that certain pelagic copepods, e.g. Pleuromma gracile 

 and Leuckartia flaviensis show phosphorescence, and that this phe- 

 nomenon is confined to definite points of their body, which correspond 

 to the ducts of certain glands of the skin of the animals. These glands 

 secrete drops of a greenish yellow substance. As long as the animals 

 lie quiet there is no phosphorescence visible, but they show this phenom- 

 enon when pressed or heated, or if brought in contact with ammonia, 

 alcohol, or glycerine. This might easily be interpreted as signifying 

 that the phosphorescence of these animals is a phenomenon, which is 

 produced by the stimulation of the animal. Giesebrecht found, howr 

 ever, that the phosphorescence occurs only when the secretion of the 

 glands is brought to the surface of the animal, and comes in contact 

 with the sea water. He proved, moreover, that the secretion even re- 

 tains its power of phosphorescing after the death of the animal. Dead 

 copepods, which had been preserved in a dry condition for three weeks, 

 still showed the phosphorescence at the opening of the glands, whenever 

 they were put into water. The above-mentioned "stimuli" caused the 

 phosphorescence only indirectly, by causing the squeezing out of the 

 secretion of the glands from the duct. 



How the contact of the secretion with water can cause the phos- 

 phorescence is not yet clear. Radziszewski f has found that a number 

 of organic compounds show phosphorescence at a comparatively low 

 temperature, e.g. 10° C, when they come in contact with atmos- 

 pheric oxygen, and the reaction is alkaline. Among these substances 

 are the soaps of oleic acid, a number of alcohols, etc. This author 

 assumes that the phosphorescence of animals is caused in the same way. 

 Traces of the phosphorescent substances and of oxygen suffice for the 

 production of the phenomenon. We can readily understand that mo- 

 tions of an animal are favorable for the production of phosphorescence, 

 as they tend to bring the oxygen (e.g. in the tracheae of insects) in con- 

 tact with new particles of the phosphorescent substance. Giesebrecht 

 questions the importance of oxygen for this process, inasmuch as in 



* Giesebrecht, Mittheilungm am der zoologischen Station zu Neapel, Vol. 2, p. 648, 

 1895. 



t Radziszewski, Liebig's Annalen der Chemie, 1880. 



