244 



KNOWLEDGE. 



[NOVEMBRR 1, 1894. 



intimate relationship between the faunas of all the southern 

 continents, and their isolation from those of the northern 

 half of the world. 



KoTE. — In the September number of Knowledge, two wood-cuts 

 illustrating Mr. Lvdekker's paper on "The Ajieient Mammals of 

 Britain" hare been transposed. Fig, 1 should be "last upper molar 

 tooth of the Uyfenarctus," and Fig. 2 should be "right upper molar 

 tooth of Steno's Horse." 



THE BACTERIA OF PHOSPHORESCENCE. 



By C. A. Mitchell, B.A.Oxon. 



THAT the flesh of certain animals, especially marine 

 fishes, could often exhibit the phenomenon of 

 spontaneous light was noticed as long ago as the 

 days of Aristotle, but it is only within the present 

 generation that the true cause has been made 

 known. 



In 1676, a Dr. Beale, of Yeavil, in Staffordshire, pub- 

 lished in the Philosophical Transactions of the Royal Society 

 a curious instance of the kind, and mentioned as" a possible 

 explanation that the stars were exceedingly bright on that 

 night, and the weather warm and gentle. A woman of 

 that town had bought a neck of veal, which seemed perfectly 

 good in every respect. On the following evening, about 

 nine o'clock, the neck of veal " shined so brightly that it 

 did put the woman into great affrightment." She roused 

 her husband, and he seeing whence the light proceeded 

 endeavoured to extinguish it by beating the veal, and 

 eventually plunging it below water ; but in vain. At last 

 he found he could extinguish the light by wiping the meat 

 with a cloth. The next day the jouit was cooked, and 

 certain neighbours who had seen it giving light were 

 invited to partake of it. All esteemed it as good as any 

 they had eaten. 



Many simOar cases of meat becoming phosphorescent 

 are on record. In 1492 it was a frequent occurrence in 

 Padua, and during the early years of last century it became 

 so prevalent in Orleans that several butchers were almost 

 ruined, since their customers considered such meat unfit 

 for food, and much of it was thrown into the river.* 

 Coming to the present day, Nuesch describes how the 

 whole of the meat in a butcher's shop became luminous in 

 one night. 



The first recorded experiments to determine the cause 

 of such cases were made by Dr. Hulme in 1800, and from 

 his results he was led to conclude : — 



1. That putrefaction was not the cause, for as decay 

 advanced the light gradually decreased. Moreover, in the 

 case of phosphorescent meat there was no offensive smell. 



2. That spontaneous light was a constitutional principle 

 of some bodies, incorporated with their whole substance 

 just as any other principle, and that it was probably the 

 first principle that escaped after the death of marine fishes. 



This plausible solution has since been displaced by the 

 discovery that bacteria were invariably present in phos- 

 phorescent sea-water and on phosphorescent meat, and that 

 directly or indirectly the light was due to their agency. 



Bacteria is the generic term applied to certain low forms 

 of vegetable life. They multiply by dividing up or "fission," 

 and some also by the formation of spores. The ijeasts, 

 which increase by budding, are accordmgly not bacteria, 

 though they are sometimes classed with them. Bacteria 

 are classified in two main groups ■.—Coccacco' or spherical 

 forms, and Bacteriacea or rod-shaped forms. To the latter 

 belong the bacteria proper, straight rod forms in which 



* " Lemery of Chvmistrv," 1720. 



spore formation is not known to occur ; the bacilli, straight 

 rod forms which form spores ; and the spirilla, twisted 

 forms not forming spores. 



An artificial growth of these on nutrient gelatine, or 

 some other suitable medium, is called a colony, and consists 

 of a mass of the organisms. The appearance of the colony, 

 which is often characteristic, is of importance in identifying 

 the species of micro-organism of which it is composed. 



At least six species of light-producing micro-organisms 

 have been described, each having different properties by 

 which they may be distinguished from one another. They 

 all belong to the bacteria proper, though, from their length 

 and breadth being often nearly the same, they have 

 occasionally been described as members of the Coccacece. 

 They fall naturally into two groups, of which the first 

 includes the four following species ; — (1 1 Bacterium phus- 

 phoresccm, a motile organism pretty widely distributed ; 

 its average size is 1-7 /xf long by 1-5 ju. in breadth; (2) 

 Bacterium Pfliigeri, an organism about the same size as 

 the preceding. It has rounded ends, and dividing rapidly, 

 the cells usually appear almost round. It is the usual 

 cause of the phosphorescence often observed on herrings 

 and mackerel. (3) Bacterium Fischeri, and (4) Bacterium 

 halticum, two species of similar size and form. They do 

 not cause any fermentation as the first two do. All these 

 may be grown on nutrient gelatine without causing it to 

 become liquid ; but for their successful cultivation they 

 require the presence of the albuminoid substance peptone, 

 and another carbon compound, such as glycerine or glucose. 

 In the second group are (1) Bacterium imlicum, a 

 motile rod of medium size, found in West Indian waters, 

 and (2) Bacterium luminosum, the cells of which are 

 shorter than those of the preceding bacterium. It occurs 

 in the waters of the North Sea. These two species are 

 able to flourish on peptone alone, and cause rapid liquefaction 

 when grown on nutrient gelatine. 



With regard to the conditions under which these various, 

 micro-organisms can produce light, it has been found that 

 temperature has a good deal of influence. According to 

 Ludwig, a piece of meat remained luminous as low as 

 - 14°. J Heated gently in a tube over a water-bath it was 

 still phosphorescent at 30°, but at 40° had ceased to emit 

 light. Bacterium phosphorescens thrives best between 15° 

 and 25°, but Tilanus and Forster proved that it could live 

 below zero. When kept at 35° for a few minutes its 

 luminosity disappeared, but on cooling returned. If, how- 

 ever, it was kept at that temperature for fifteen minutes 

 its power of producing light was permanently lost. 



The other organisms show a difference in this respect. 

 B. i-^sr/icri' gives no light at a temperature above 25^, while 

 B. indicum, which thrives best at 80°, cannot grow 

 below 15°. B. luminosum, on the other hand, is most 

 luminous at 15°. 



There is also a difference in the character and intensity 

 of the light produced by the various species. B. phos- 

 phorescens gives out a greenish-yellow light, while that 

 produced by B. PrUhjeri is bluish-white and far more 

 intense. By exposing a sensitive plate in an otherwise 

 completely dark room, Forster succeeded in obtaining a 

 photograph of a colony of this species by means of its own 

 light. Fischer was able to do the same with colonies of 

 B. indicum. It is, therefore, not surprising to learn that 

 Ludwig,. who examined spectroscopically the light produced 

 by B. PfliJgeri, obtained a spectrum rich in violet rays. 



t 1 '' = Too^oootli part of a metre = -j^^th of an inch. 



J All the degrees of temperature are on the Centigrade scale. To 

 convert into Fahrenheit, midtiplv the number of degrees by 1'8, and 

 add 32 to the product. 



