The Microscope. 341 



Luminous bacteria.* — It would seem as if the influence of 

 bacteria and mici'O-organisms generally upon higher forms of 

 life was only just beginning to be understood. The researches 

 of naturalists are constantly bringing new and unexpected facts 

 to light. For instance, there is nothing better known than 

 that phosphoresence is frequently exhibited b}^ marine animals, 

 especially by the Crustacea. This phosphorescence is often in- 

 fectious, that is, it can be communicated by touch. A French 

 naturalist, M. Giard, has recentl}- made known the results of 

 some observations and experiments that he has been making 

 with Talitrus and other marine Crustacea On microscopically 

 examining a brightly phosphorescent specimen which he found 

 on the beach walking slowly instead of leaping as is its usual 

 habit, he traced the phosporcscent light to the presence of bac- 

 teria in its muscles, which were greatly altered. On inoculating 

 other and healthy individuals of this and other species, the 

 same disease was produced amongst them, and M. Giard says 

 that his laboratory was quite lit up at night with these lumin- 

 ous but diseased Crustacea. The inoculation was continued to 

 the sixth generation apparently without any attenuation of the 

 microbic action. The disease seems to follow a regular course, 

 and the crustaceans die in three or four days. The phosphor- 

 escence, however, always lingered a few hours after death. 

 Crabs were inoculated in the same way. 



Why the eyelashes are sometimes seen in the eye-piece. f — 

 Meslin explains the reason why one sometimes sees in the 

 bright circle of light i.i the microscope the image of his own 

 eyelashes, inverted or erect, according to the kind of eye-piece 

 used. The explanation lies in the fact that the lashes produce 

 in the cone of light which proceeds from the mirror a shadow 

 figure, the projection of which upon the retina depends on the 

 focus of the rays issuing from the ocular. If these be a little 

 convergent, or the eye be far enough from the ocular, the image 

 will be thrown behind the. retina; accordingly, a seemingly 

 inverted image appears. In the reverse condition (strong con- 

 vergence of the rays issuing from the ocular, or a near position 



* Science Gossip. 



t Journ. R. M. Soc. from Jourii. cle Phys. 



