62 THE NATURE OF ANIMAL LIGHT 



have found penetrating radiation in luminous forms. It 

 seems that certain kinds of cardboard, especially yellow 

 varieties, or wood, will give off vapors that affect the 

 photographic plate. The action is especially marked with 

 damp cardboard at a temperature of 25°-35° C, and 

 Dubois and Muraoka must have used such cardboard to 

 cover their plates. A piece of old dry section of beech 

 or oak trunk, placed on a photographic plate for 15 hours 

 in a totally dark place, will register a beautiful picture of 

 the annual rings of growth, medullary rays, junction of 

 bark and wood, etc. Eussell (1897) had previously found 

 that many bodies, both metals and substances of organic 

 origin (gums, wood, paper, etc.), placed in contact with 

 photographic plates, would affect them, and concluded 

 that vapors and not rays were the active agents. As a dry 

 piece of wood has a very definite smell, there is something 

 given off which can affect our nose and there is no reason 

 why it should not change, by purely chemical action, the 

 photographic plate. This action of wood on the plate is 

 prevented by interposing a sheet of glass. Frankland 

 (1898) has described similar vapors coming from colonies 

 of Bacillus proteus vulgaris and B. coli communis which 

 affect a photographic plate laid directly over the colonies 

 in an open petri dish. There is no effect if the glass cover 

 of the petri dish is between plate and bacteria. There is, 

 then, no specific emission of X-rays or similar penetrating 

 radiation from luminous tissues which will affect the pho- 

 tographic plate through opaque screens. 



A similar conclusion is reached if we attack the prob- 

 lem in another way. X-rays and radium rays (Becquerel 

 rays) cause fluorescence of ZnS, barium platinocyanide. 



