ON SOME NEW MICRO-ORGANISMS OBTAINED FROM AIR. 
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Broth .—After seven days (August 17—24, 1886) the liquid is clear, excepting the 
surface, on which there is some thin, granular, floating matter, and at the bottom there 
is a small amount of whitish deposit. 
Appearance on plate-cultivation .—The surface-colonies are seen with the naked eye 
to form an opalescent expansion of increasing size, with a very irregular contour. (See 
Plate 18, No. 2 cl.) In the depth of the gelatine, on the other hand, the colonies 
appear as grey clots. Under a low power (X 100) the surface-colonies exhibit a dense 
centre, surrounded by a very thin and granular expansion having a highly irregular 
contour. (See Plate 18, No. 2b.) The drawing represents a colony in which this 
surface excrescence is commencing. No. 2c represents a colony in the depth of the 
gelatine. Viewed against the light, these surface-colonies are of a beautiful azure- 
blue colour. 
8. Bacillus Pestifer. 
Occurrence .—This was found forming a small white expansion on the surface of a 
gelatine-dish which had been exposed to the air in a garden near Hughenden, 
Bucks. 
Microscopic appearance .—Under a high power this is seen to be a large thick 
bacillus about 3'4/r in length and from '8 g to 1'7/r in thickness; the length is 
difficult to determine, owing to the formation of threads, which are frequently of 
great length, extending far beyond the field of the microscope, and giving rise to 
winding vermiform figures. (See Plate 19, fig. 7, No. 7b.) 
Viewed in drop-cultivations, the bacilli are seen to exist singly, in pairs, threes and 
fours, &c., up to exceedingly long threads. Their movement is slow and undulating, 
the single bacilli exhibiting most motility. It also forms non-motile tangled masses, 
but in no case was spore-formation observed. In Plate 19, No. 7c, which is 
drawn from a drop-cultivation, the arrangement of the bacilli in smaller groups is 
shown. Although we have examined a very large number of preparations of this 
organism, both in young and old cultivations, in gelatine, agar-agar, and broth, we 
have never observed any spore-formation. 
Appearance in Cultivations. 
Gelatine .—On the surface it produces an almost colourless feathery expansion, 
which causes slow liquefaction of the gelatine. 
Agar-agar .—Commences by forming a grey-white smooth surface-growth, which 
rapidly extends over the agar ; the surface-growth sometimes becomes very much 
wrinkled, like that of the Bacillus subtilis (see below), but it has a more moist and 
shining appearance than the latter, and is of a grey, transparent, almost colourless 
hue. The wrinkles are very highly convoluted and twisted. (See Plate 19, No. 7a.) 
Broth .—After four days (August 31—September 4, 1886) the liquid is slightly 
