Il6 BIOLOGICAL LECTURES. 



steady application of fresh air upon it by the action of the 

 bellows. 



The fact that the illumination of the cell is due to the action 

 of oxygen may be shown in a simple way by putting the slide 

 on which the luminous organ has been crushed, and the photo- 

 genic material spread out, into a jar containing carbon dioxide. 

 The light disappears almost instantly ; but if the same slide be 

 placed in a jar containing oxygen, or simply exposed to air, the 

 light comes back, and lasts as long as the luminous material, 

 a certain amount of moisture, and other necessary conditions 

 are present. 



This process can be repeated several times, showing conclu- 

 sively that the light-giving material itself is quite independent 

 of cell-life, although it owes its existence primarily to the life 

 activity of the cell as a whole. 



The luminous phenomenon, wherever it occurs, is apparently 

 carried on by essentially the same process throughout the 

 animal kingdom. In air-breathing organisms, such as the 

 fire-fly, the product of cell metabolism is oxidized in situ by 

 the oxygen of the inspired air. In some marine organisms the 

 secretion is often thrown out in the form of liquid from the 

 gland to the surrounding medium, and the oxidation is accom- 

 plished by the oxygen dissolved in the sea water. In luminous 

 Salpa the photogenic granules formed in the blood-corpuscles 

 are oxidized by the oxygen dissolved in the blood plasma. 



Perhaps I can summarize the preceding, and make my point 

 more intelligible by the help of a diagram. 



We have seen that the essential bases for the luminous 

 phenomena of the living organism consist (i) in the production 

 of a certain chemical substance in the cell, which recalls to our 

 mind the well-known series of phenomena in the process of 

 secretion ; and (2) the oxidation of this substance by the 

 oxygen brought in from without, and thus making the cell a 

 new center of disturbance to the surrounding ether. 



