66 BIOLOGY AND TECHNIQUE 



The development of the organism is slow and sparse, and is directly 

 inhibited by the presence of organic matter. It is strongly inhibited 

 by the presence of ammonia. 



The Liberation of Energy by Bacteria. Like all other living 

 beings, bacteria in their metabolic processes liberate energy. It has 

 been shown by several observers that slight quantities of heat are 

 given off from actively growing cultures. The functions, further- 

 more, of reproduction, motility, and enzyme formation may be looked 

 upon as forms of energy liberation. In addition to this, certain 

 bacteria have been observed which may liberate energy in the form 

 of light. 



Light Production by Bacteria.- -The production of light by bac- 

 teria is a power possessed chiefly by certain species inhabiting salt 

 water. Thus, much of the phosphorescence observed at sea, though 

 more frequently due to Medusa and other invertebrate animals, is 

 caused by these bacteria. Numerous species which produce this 

 phenomenon have been isolated, too many, and too unimportant, 

 to be individually described. All of them are aerobes and require 

 highly complex food stuffs. They are closely allied to the putre- 

 factive bacteria, and in the sea are usually found upon rotting 

 animal matter. 30 The production of light seems directly dependent 

 upon the free access of oxygen, since no light appears under 

 anaerobic conditions. Their luminous quality, moreover, is not a 

 true phosphorescence, in that it does not depend upon previous 

 illumination and develops as well in cultures kept in the dark as 

 in those which have been exposed to light. 31 



The Formation of Pigment by Bacteria (Chromobacteria) . A 

 large number of bacteria, when cultivated upon suitable media, give 

 rise to characteristic colors which are valuable as marks of differen- 

 tiation. For each species, the color is usually constant, depending, 

 to a certain extent, upon the conditions of cultivation. In only a 

 few of the pigmented bacteria is the pigment contained within the 

 cell body, and in only one variety, the sulphur bacteria, does the 

 pigment appear to hold any distinct relationship to nutrition. In 

 most cases, the coloring matter is found to be deposited in small 

 intercellular granules or globules. The absence of any relationship 

 of the pigment to sunlight, as is the case with the chlorophyll of 



^Pfliigcr's Arch. f. Phys., xi, 1875. 

 31 Fischer, Cent. f. Bakt., iii, 1888. 



