CONTRACTILITY AND PHOSPHORESCENCE. 191 



is devoid of heat. The organism may live in water of freezing 

 temperature, yet it is perfectly possible that there is enough 

 difference of temperatures in different parts of the living cell 

 to serve as a stimulus for the contraction of the protoplasm. 



III. 



Now, coming to the third and concluding part of the paper, 

 viz., the relationship of protoplasmic contractility and phos- 

 phorescence, we may note at the outset that the distinction 

 drawn between heat and light is purely of an artificial charac- 

 ter. They are simply variations of the same radiant energy. 

 Their difference objectively considered is simply that of degree 

 and not of kind. The wave-length of the one is a little longer 

 than that of the other. If they appear to be so different to us 

 as heat and light, the trouble lies in our organization, and not 

 in the nature of original radiant energy. The difference is 

 subjective and not objective. 1 The heat-producing particles 

 and the light-producing particles, objectively considered, may 

 not be very different from each other. They may be variations 

 of similar chemical siibstances, as tJie resulting energies, the prod- 

 ucts of tJieir oxidation, are the variations of tJie same radiant 

 energy. They may be very nearly related in chemical struc- 

 ture as well as in anatomical origin ; they may exist in one and 

 the same cell, as the products of "secretion " or of the metab- 

 olism of the cell. 



The stimuli, therefore, such as mechanical jars, shocks, agi- 

 tation, nervous impulse, etc., which induce combustion of the 

 thermogenic molecules, may also be presumed to incite combus- 

 tion of the photogenic molecules as well, which exist side by 

 side. 



When there is a muscle in which these two varieties of oxi- 

 dizable substance exist side by side, then we have contraction 

 as well as phosphorescence at the same time. From one vari- 

 ety of granules, heat is generated, which becomes converted 

 into the mechanical work of contraction ; from another, light, 



1 See in this connection my previous paper, " On the Physical Basis of Animal 

 Phosphorescence," Biological Lectures, 1895. 



