452 Transactions of the Society. 



to melt in a room without a fire. On the second day a faint scum 

 was visible on the surface in patches, enveloping grey, soot-like 

 particles. Some of this pellicle seen under the Microscope showed 

 very pale, motionless organisms lying in it, resembling rather 

 elongated micrococci. The water was left further undisturbed for 

 another day, but furnished no appreciable difference except greater 

 distinctness of the imbedded organisms. Some of the pellicle was 

 stained with aniline blue, and mounted in acetate of potash solution 

 without having been dried. Whether from want of refractive 

 differentiation between the objects and mounting medium, or from 

 the acetate of potash acting upon the pellicle, the outlines of the 

 minute organisms were indistinct ; consequently a different method 

 was adopted, which seemed to offer advantages. A speck of the 

 pellicle was placed, with as little disturbance as possible, in a 

 droplet of distilled water on the cover-glass, then, as recommended 

 by different observers, dried over a flame, in this case very slowly. 

 Afterwards it was covered with the following staining fluid and 

 protected from the dust : — 



Bismarck or aniline brown (of German make), 4 grains ; citric 

 acid, 16 grains; distilled water, 200 minims; boiled in a test-tube, 

 cooled, filtered, reboiled, and a trace of carbolic acid added. 



After being covered with the staining medium for an hour it 

 was washed with distilled water by tipping off the fluid, draining 

 closely on blotting-paper, repeating this until the water was 

 colourless, then drying again by gentle heat and mounting the cover 

 dry. 



Previously I tried the aniline brown without the citric acid, 

 but the addition of the latter appeared to facilitate the washing 

 by increasing the solubility of the colouring agent without lessen- 

 ing the staining qualities. 



Great care was required if the specimens were washed with 

 the cover on the slide, for the least displacement caused the pellicle 

 with its organisms to roll up into continuous lines. 



I am not prepared to say that the method of drying does 

 not slightly shrink the objects. I fear it does, though I do not 

 think more than osmic acid, as the substance enveloping the 

 organisms appears indistinctly afterwards. The minute bodies 

 found in the melted hail differed most completely from those of 

 the frozen rain-water. In parts where but little disturbance of 

 the pellicle occurred upon removal for examination, the organisms 

 were seen lying very irregularly near to each other, whilst 

 in what appeared to be a second pellicle formed just beneath 

 the outer one, they occurred mostly in rows, and are often at 

 rather an acute angle with one another. In size they differed, 

 doubtless owing to being in various stages of growth and fission. 



