THE RE-ACTIONS OF ORGANIC MATTER ON FORCES. 49 



change. In the body this connexion of phenomena is the 

 same as we see it to be out of the body. Just as in a burn- 

 ing piece of wood, the heat given out by the portion actually 

 combining with oxygen, raises the adjacent portion to a tem- 

 perature at which it also can combine with oxygen; so, in a 

 living animal, the heat produced by oxidation of each portion 

 of organized or unorganized substance, maintains the tem- 

 perature at which the unoxidized portions can be readily 

 oxidized. 



§ 19. Among the forces called forth from organisms by 

 re-action against the actions to which they are subject, is 

 Light. Phosphorescence is in some few cases displayed by 

 plants — especially by certain fungi. Among animals it is 

 comparatively common. All know that there are several 

 kinds of luminous insects; and many are familiar with the 

 fact that luminosity is a characteristic of various marine 

 creatures. 



Much of the evidence is supposed to imply that this evolu- 

 tion of light, like the evolution of heat, is consequent on 

 oxidation of the tissues or of matters contained in them. 

 Light, like heat, is the expression of a raised state of molecular 

 vibration: the difference between them being a difference in 

 the rates of vibration. Hence it seems inferable that by 

 chemical action on substances contained in the organism, heat 

 or light may be produced, according to the character of the 

 resulting molecular vibrations. Some experimental evidence 

 supports this view. In phosphorescent insects, the con- 

 tinuance of the light is found to depend on the continuance 

 of respiration; and any exertion which renders respiration 

 more active, increases the brilliancy of the light. Moreover, 

 by separating the luminous matter. Prof. Matteucci has 

 shown that its emission of light is accompanied by absorp- 

 tion of oxygen and escape of carbonic acid. The 

 phosphorescence of marine animals has been referred to 

 other causes than oxidation; but it may perhaps be exr 



