18 THE ZOOLOGIST. 



daylight in the Mediterranean may be cited as a source of allure- 

 ment with as much reason as its luminosity. 



Besides the phosphorescence of living fishes there is another 

 and even more familiar manifestation of this property in fishes 

 within twenty-four hours after death, and which has given rise to 

 many interesting experiments, such as those of Kobert Boyle on 

 dead Whitings,* and of Dr. Hulme on Herrings.! This is now 

 known to be due to the presence of photogenic Bacteria which 

 occur exclusively in sea-water. In the paper just quoted Bobert 

 Boyle mentions that he placed a luminous Whiting in the 

 receiver of an air-pump, and found that it shone less on extract- 

 ing the air. On being replaced in air it shone brightly. Dr. 

 Nathaniel Hulme, again, demonstrated that the luminous con- 

 dition of the Herring and the Mackerel disappeared on putre- 

 scence. He made a luminous solution from the fishes composed 

 of two ounces of Epsom salts or " vitriolated " magnesia in two 

 ounces of cold spring water. He extinguished the light of the 

 luminous Herring by freezing, but it returned on thawing. 

 Roasting and boiling extinguished the light, which did not 

 return. It is curious to find that he regarded the light as a 

 constituent principle of marine fishes, and that it is separated 

 by the menstrum fitted to decompose it. He was further of 

 opinion that no offensive putrefaction takes place in the sea, 

 and that the flesh of marine fishes remains sweet for some time, 

 and provides nourishment for other forms — an evident instance, 

 he thought, of the wisdom of the Creator. Dr. Hulme appa- 

 rently never had the opportunity of coming in contact with a 

 mass of putrescent herrings drawn up by a trawl from the 

 bottom of the sea. 



These early experiments are quite consistent with what is 

 now known, viz. that the luminosity of fishes after death is due 

 to photogenic Bacteria. One of the best known and most widely 

 distributed forms is a short thick bacillus (Photobacterium pJios- 

 phorescens), an excellent account of which, with others, is given 

 by Mr. J. E. Barnard. \ These Bacteria are marked by a 

 tendency to undergo involution and by polymorphism, some 



* Philos. Trans. 1667, pp. 591-93. f Ibid., 1800, p. 161. 



I Jenner Instit. Prev. Med., 2nd ser., August, 1899, pp. 81-112. Two 

 plates. 



