May, 1911. 



KNOWLEDGE. 



191 



FiGURr 



A flask photographed by the Ught 

 of the bacteria within. 



uot all emit the greatest possible amount of light unless an 

 increased quantity of saUne matter is present. It was 



recognized that prob- 

 ably in sea - water 

 would be found the 

 necessary constituents 

 for an artificial medium, 

 and after a series of 

 f.\periments that which 

 best suits them is found 

 to be an ordinary gelatin 

 one to which has been 

 added 2- 75 per cent, of 

 sodium chloride. ■ 75 per 

 cent, of potassium chlo- 

 ride, and -25 per cent, 

 of magnesium chloride. 

 It is important that 

 the medium should be 

 neutral, or very slightly 

 alkaline: an acid 

 medium is entirely un- 

 suitable fortheir growth. 

 The most easily procured organism of this group is the 

 Photobacterium phosphorcsccns. It may be obtained 

 from a dead herring or mackerel. The 

 fish should not be washed in fresh water 

 after being caught. It should be placed 

 in a closed receptacle, such as a large- 

 sized Petri dish, for about twenty-four 

 hours at approximately 20' C. At the 

 end of this period there will probably be 

 some spots which phosphoresce brightly. 

 Plate cultures may be made from these 

 spots, and in three to four days at 

 ordinary room temperature the plates, 

 on examination in the dark, will probably 

 show some luminous colonies. Sub- 

 cultures may be made from these, and 

 the organisms may be kept going in 

 artificial cultivations on the medium 

 mentioned for several weeks without 

 difficulty. Fish-broth or peptone-beef- 

 broth may be substituted for a solid 

 gelatin medium. It is necessary, how- 

 ever, if brightly luminous fluid cultures 

 are required, to resort to some 

 method of aeration, a supply of free 

 oxygen being essential. In any case, 

 when making fluid cultures, the media 

 should be thoroughly well shaken up to 

 ensure that as much oxygen as possible is 

 present in solution before the organisms 

 are inoculated into it. If the maximum amount of luminosity 

 is aimed at. oxvgen may be allowed to bubble slowly through 

 the medium directly any luminosit}' appears, and although 

 ^— the period over which 



J the light production 



V occurs is thereby re- 



duced, the luminosity 

 is extremely brilliant 

 while it lasts. 



Figure 1 shows a 

 flask of these organisms 

 photographed by means 

 of their own light, which 

 will gi\e some idea of 

 the brilliancy to be 

 obtained under these 

 conditions. 



Figure 2 is a 

 photograph of Lord 

 Lister, illuminated by 

 means of growths on 

 solid media. On each 

 side will be seen 



Figure 3. 



Colonies of bacteria on a Petri dish 

 photographed by their own light. 



FlGlRE 4. 



Pliotobacte rill til balticum grown 



in fish-broth. 



tubes containing the organisms and several of them 

 were placed underneath throwing the light upwards. 



Figure 3 is an ^^m-^ 



ordinary Petri dish with 

 luminous colonies on it. 

 These again were photo- 

 graphed entirely by their 

 own light, the colonies 

 standing out brilliantly 

 on a dark back-ground. 

 The exposure in photo- 

 graphing these organ- 

 isms is always some- 

 what prolonged; 

 although their visual 

 luminosity is high yet 

 their photographic 

 action is not rapid, as 

 the light emitted does 

 not lie in that portion 

 of the spectrum which 

 is photographically 

 most active. There is 

 the further difticulty that the light happens to lie in a region 

 of the spectrum to which photographic plates are particu- 

 larly insensitive, so that due allowance 

 must be made for these two factors 

 if any attempt is made to obtain a 

 photograph of these organisms by their 

 own light. 



Some twenty-five varieties of these 

 organisms have been described, and it 

 is also stated that other bacteria such 

 as the Cholera vibrio, are known to 

 produce light under certain conditions. 

 Of these twenty-five described species 

 it is more than likely that some are not 

 really entitled to be regarded as distinct. 

 A broad classification of them may be 

 made by separating those that grow at 

 low, and those that grow at a higher 

 temperature. There are two or three 

 species found in Northern latitudes that 

 thrive and produce light at 0°C., 

 whereas there are certain other varie- 

 ties which grow in Southern latitudes, 

 particularly in the Indian Ocean, that will 

 go on producing light at a temperature 

 of from 30"C to 35"C. The writer has 

 had through his hands at various times 

 some fourteen varieties, as well as one 

 which there is reason to think is a new 

 species, originally identified at the Marine 

 Biological Laboratory, Plymouth. Morphologically the 

 organisms vary widely: the common species Photobacterium 

 phosphorescens already mentioned, is a short thick rod, 

 which when grown on 

 a medium containing 

 more than three per 

 cent, of saline matter 

 assumes a much 

 shorter, thicker appear- 

 ance, and is almost 

 coccoid in form. Nearly 

 all \arieties change ? 

 considerably in form 

 when artificially culti- 

 vated for long periods, 

 so that it is often 

 difficult to identify :i 

 particular species by 

 its microscopic appear- 

 ance. Owing also to the 

 amount of saline matter 

 necessary in the med- 

 ium, the organisms 



Figure 2. 



A picture of Lord Lister illuminated 



bv bacteria. 



Figure 5. 



Photobacterium balticum grown 

 in peptone-beef- broth. 



