TRANSACTIONS OF SECTION K. 801 



3. On Luminous Bacteria. By J. E. Barnard and Professor Allan 



Macfadyen, M.D. 



Many instances of light-production occur in nature amongst plants and animals. 

 This luminosity is most striivingly exhibited hv marine animals and bv minute 

 vegetable-cells belonging to the group of the suicteria. Light-production by living 

 protoplasm is a process intimately bound up with the life of the organism, as in 

 the case of the luminous bacteria. The luminosity of mineral and other inert 

 bodies is dependent on an extraneous light source. 



Amongst light-producing organisms our knowledge of the process is most 

 exact in the case of the bacteria. Their simple semicellular structure, and the fact 

 that modern bacteriological methods enable us to isolate and study particular 

 organisms, renders it somewhat more easy to study the conditions under which 

 light-production can best occur. The observations which are embodied in tliis 

 paper were made on luminous bacteria. These organisms are to be found mainly 

 in sea-water and on dead marine animals. They are widely distributed in this 

 respect. We have obtained and studied the most important types. About 

 twenty-five varieties have been described, but it is probable that some of these are 

 very closely related, if not identical. A hitherto undescribed form has been 

 isolated from sea-water in the course of investigations made by one of us at 

 Plymouth. It belongs, like most of the other species, to the group'of the bacilli. 

 The temperature conditions as regards growth vary considerably, and ran^e from 

 zero to 37" C. 



The luminosity of the sea is mainly due to higher forms of marine life and not 

 to bacteria, at any rate in northern latitudes. On the otlier hand the phos- 

 phorescence of dead objects, such as fish, &c., is due to bacterial forms of life. 



We have not been able to confirm the statements that luminous bacteria have 

 direct infective properties as regards crabs and other marine animals. 



These organisms require particular and exact conditions in order to exhibit 

 their luminous properties. They must have a suitable nutrient soil containing 

 such proportions of salts as shall render the medium isotonic. For example, sodic 

 chloride, if present to the extent of 3 per cent., will render the organisms luminous 

 and ensure their remaining so for some time. In this manner tliey can be readily 

 cultivated and studied in the laboratory. 



The luminosity appears to be a function of the living cell and can be disturbed 

 by any process which interferes with the vitality of the cell itself. The dead cell 

 is non-luminous, whilst antiseptics which kill the cells inhibit at the same time 

 their luminosity. 



A supply of free oxygen is essential ; in the absence of oxygen the organisms 

 live but are non-luminous. There is no evidence of a bacterial product as the 

 source of the light. The process appears to be the result of an active oxidation 

 occurring within the cell. The light produced is confined to a small portion of 

 the visible spectrum, and invisible radiations have not been detected. As the 

 spectrum of none of these luminous organisms extends even to the red, it may 

 .safely be assumed that no heat radiations are emitted. The light is produced 

 without heat. No invisible radiations allied to the X-rays were detected. Photo- 

 graphs have been obtained by the aid of the light emitted by these organisms. The 

 time-exposure required is, however, considerable. 



An exposure to the temperature of liquid air does not destroy the luminosity 

 of the organisms. It has been found possible to triturate bacteria at the tempera- 

 ture of liquid air by means of special methods devised at the Jenner Institute of 

 Preventive Medicine. The luminous bacteria mechanically broken up in this 

 manner ceased to phosphoresce. The luminoijity, therefore, is due to the vital 

 processes of the cell, and essentially depends for its origin on the intact organisa- 

 tion of the cell. 



We have brought these results forward because this interesting group of 

 organisms have not hitherto been studied in this country so far as we can trace. 



1902; 3 p 



