RADIANT ENERGY 413 



Heat is the most familiar form df radiation from organisms. 

 It is so familiar that we take it for granted. 



Luminescence among insects and fish is not uncommon — the 

 firefly is known to all. The sources of this light are two. Lumi- 

 nous bacteria may be responsible. This is true of certain tropical 

 fish the light organs of which are colonies of luminous bacteria. 

 The fish thus has nothing to do with its light, which goes on 

 shining interminably. Usually, luminescence in organisms is 

 due to a reaction between the two chemicals which duBois called 

 luciferin and luciferase. When these come into contact, light 

 results. E. N. Harvey has extended this work. 



Fluorescence in physical systems was first interpreted by Stokes 

 in 1852. Helmholtz soon after made a study of the fluorescence 

 of the lens of the eye and considered the wave lengths, 3,000 to 

 4,000 A. U. to be the most effective in producing the effect. 

 Fluorescence is the transformation of light from that form which 

 illuminates matter into that radiated from it, so that the radiated 

 light is of a different (greater) wave length. Fluorescence in 

 organisms has received considerable attention of late from F. E. 

 Lloyd, who has found that the blue-green algae, the diatoms, and 

 some of the green algae (the Pleurococcaceae) are strongly 

 fluorescent when viewed ultramicroscopically with a dark-field 

 condenser, if the proper optical conditions are achieved. The 

 fluorescence is due to phycocyanin rather than to chlorophyll. 

 Lloyd has also reported fluorescence in a number of other uni- 

 cellular organisms. He found Paramoecium, Oxytricha, and 

 certain bacteria to fluoresce in monochromatic light. 



Phosphorescence is another form of radiation from living things. 

 Phosphorescence, where due to exposure to heat, light, or 

 electricity, differs from fluorescence in that it continues after 

 illumination has ceased. Where due to phosphorus, it is the 

 result of oxidation. It is in this form that it is best known in 

 organisms. It is to be observed particularly in minute marine 

 organisms which at night may make the oar of a rowboat resemble 

 a flaming torch in the water. 



Electricity is a form of energy released by hving matter to 

 which reference has already been made (page 355). 



Gurwitsch Rays. — The foregoing types of radiation are rather 

 familiar and have long been known. They are, therefore, not 

 questioned, and as something of their physical and chemical 



