CHAPTER X 

 TISSUES OF PHOTOGENESIS OR LIGHT-PRODUCTION 



PROTOPLASM can produce not only heat, motion, and electricity, as was 

 seen in the preceding pages, but it can produce light as well. This power 

 is found in a limited number of organisms that are somewhat more 

 numerous and much more widely distributed in the animal kingdom 

 than are creatures that produce electricity. 



The power is probably a specialization of the same or similar pro- 

 cesses to those that produce heat, motion, and electricity. Briefly, it 

 consists of the production of a material that, when exposed to the action 

 of oxygen, or possibly some other substance, rapidly unites with it, and 

 in doing so gives rise to light waves. 



The light that they produce may differ in color and quantity, accord- 

 ing to the animal that produces it, from a green light to various shades 

 of red, purple, and violet. In some forms, several colors or shades are 

 emitted by the same organ at different times or by different organs on the 

 same animal. It is possible that some creatures give out a light that is 

 not visible to the human eye, although it may stimulate the eyes 

 of other forms whose eyes are adapted to perceive it. 



The substance that thus gives light upon oxidization is of unknown 

 chemical formula. Du Bois has extracted it from the tissue, probably 

 in a very impure state, and has made it produce the light. He has 

 applied the name luciferase to it and maintains that it is not with oxygen 

 that it must combine to produce the light, but with another substance 

 in the blood, to which he has applied the name luciferine. His theory 

 is not considered proven, and oxygen is probably the reducing agent. 

 This oxygen may be brought to the scene of action in some unstable 

 compound, as haemoglobin, for a carrier. Phosphorus forms no im- 

 portant part of the luciferase, as we shall call the light-giving secretion, 

 using one of Du Bois's names without accepting his theories. 



Luciferase is a secretion, the product of protoplasmic activity in chang- 

 ing the food materials brought to it into some specific substance of use 

 to the organism. It can be seen in sections and teased cells, as a collec- 

 tion of granules that stain very readily and retain the stain with great 

 tenacity. Sometimes it remains within the cell and is used in situ, the 

 oxygen being brought to it. At other times it is discharged from the 



