1895.] MICROSCOPICAL JOURNAL. 223 



while the dark slide with the sensitive plate is being inserted 

 and the slide drawn. The shutter in front of the mirror is now 

 raised, and an exposure of 30 to 45 seconds is made if with lamp- 

 light, or of 5 to 15 seconds if with daylight. 



Seeing Air- Borne Spores. — At the April meeting of the 

 Calcutta Microscopical Society, Mr. W. J. Simmons described 

 his method of making an observation of dust with the view of 

 detecting in it the air-borne spores which are said to cause 

 moulds to grow in a manner which the earlier observers be- 

 lieved favored the doctrine of spontaneous generation. The 

 method is simplicity itself, and consists in placing a drop of 

 pure glycerine on the centre of a slip of glass measuring three 

 inches by one inch. The drop is smeared over the glass lightly 

 so as to cover a surface of about three-quarter inches in diame- 

 ter, and is then exposed to the air for two or three days. When 

 the dust which settles on the smear is to be examined under 

 the microscope, a circular cover glass is placed on it, and the 

 deposit is now shown by the microscope to be composed of a 

 most heterogeneous collection of objects. Fibres of all sorts, 

 the scales from insects, wings, root, pollen, starch, down, frag- 

 ments of epidermis, and of the cuticle of plants, hair, entire 

 mites, numberless inorganic particles, charred straw, portions 

 of insects, hairs from plants, and several spores of fungi are 

 thus revealed. 



If a drop of glycerine, half an inch in diameter, arrests so 

 many spores, how many do we inhale daily, and how many are 

 deposited on our food in the course of a day ? The study of 

 dust is not one suited to a beginner in microscopy, because it 

 presupposed familiarity with the thousand and. one objects 

 which are certain to be present on the glass slip; but it pre- 

 sents no insuperable difficulties, and does not demand any spe- 

 cial or costly appliances. 



BIOLOGICAL NOTES. 



Sand Fly. — These pests are found on the Florida sea coast. 

 While mosquitoes at times may make a person forget all his 

 other trouble, the sand fly will make him think he has added a 

 new one. The principal feature of interest is their bill, short 



