98 MOLAR AGENTS AND PROTOPLASM [Ch. IV 



molecular changes in chemical compounds. Certain substances 

 have a specific rate of vibration, so that when this is reproduced 

 by a vibrating cord or plate, explosion of the substance may 

 occur. Iodide of nitrogen is one of these substances which is 

 exploded by a high note. (Champion and Pellet, '72, p. 212.) 

 Upon this property of explosive compounds depends, apparently, 

 the efficacy of "detonators," the explosion of a small quantity 

 of which is capable of producing the explosion of a great mass 

 of a second compound. Living protoplasm is, likewise, espe- 

 cially affected by periodic disturbances, and it is doubtless due 

 to the peculiarities of its chemical structure that the auditory 

 epithelium is so affected by sound waves in all their modifica- 

 tions of pitch, volume, and timbre. 



§ 2. Effect of Molar Agents upon the Metabolism 

 AND Movement of Peotoplasm 



We shall first consider the effect on metabolism, and then on 

 movement. The principal metabolic effects that will be con- 

 sidered are phosphorescence and secretion. 



The phosphorescence of organisms is usually regarded as a slow 

 combustion (oxidation) of organic substances. This chemical 

 process is apparently accelerated by mechanical irritation, as 

 every one must have noticed who has rowed a boat on a quiet 

 summer's evening upon the sea. At every stroke of the oar, 

 a gleam is sent along its length. An analytical study of this 

 phenomenon has been made by Massaet ('93, p. 62). When 

 a drop of water containing Noctiluca is put on filter paper, and 

 the liquid is absorbed, there comes a moment when the surface 

 film of the water flattens the spherical body of Noctiluca. At 

 that moment of pressure light is emitted. If, however, the 

 water is put into a slight vibration by a needle attached to a 

 tuning-fork, and if the agitation is insufficient to deform the 

 body, no light will be given forth. Deformation of the body, 

 but not slight agitation, is, consequently, accompanied by those 

 metabolic processes which result in the production of light. 



Secondly, contact may induce the production and discharge 

 of secretions. Verworn ('89, p. 81) has called attention to 

 this phenomenon in the cases of Actinosphserium and Thalassi- 



