THE MICRO-ORGANISMS PRESENT IN THE ATMOSPHERE. 
137 
3 colonies must therefore be subtracted from No. 1 and 4 from 2. 
Thus 
10 litres of air yielded, therefore, in 
No. 1 (sugar-wool), 37 colonies. 
No. 2 (glass-wool), 34 ,, 
IV. Roof of Science Schools. October 8, 1886. Wind S.W., very gentle. Hoads 
wet, pavement dry. 4.46 p.m. to 5.34 p.m. 15 0, 6 C. 
Comparison between glass and sugar plugs. 
No. 1. Volume of air =18 litres. 
Construction of plugs. — (a) Glass ivool only. 
(If) Sugared glass-wool and sugar-powcler. 
Rate. —5’7 strokes per minute. (Tube exposed 11 minutes.) 
„ , . . n .. . . f 22 moulds. 
Colonies m flasks .— (a) 25 j ^ 
(h) 0. 
No. 2. Volume of air = 21 litres. 
Construction of plugs. — (a) Sugaredl glass-wool only. 
(b) Sugared glass-wool and sugar-powder. 
Rate. —5'7 strokes per minute. (Tube exposed 15 minutes.) 
7 . . n 7 , . f 16 moulds. 
Colonies m flasks. —(a) 22 j ^ ^ 
. < h) °* 
Control-tube, containing plug of sugared glass-wool only, exposed 53 minutes; 
flask contained 0 colonies. 
10 litres of air yielded, therefore, in 
jNo. 1 (glass-wool), 14 colonies. 
[No. 2 (sugar-wool), 10 ,, 
V. North Chemical Laboratory. October 9, 1886. After departure of students. 
Empty. 5.26 p.m. to 6.8 p.m. Nos. 1 and 2 alternated in aspiration 
No. 1. Volume of air =18 litres. 
Construction of plugs. — (a) Glass-wool only. 
(b) Sugared glass-wool and sugar-powder. 
Rate. — 5'7 strokes per minute. (Tube exposed 12 minutes.) 
48 moulds. 
0 liq. 
2 moulds. 
.0 liq. 
No. 2. Volume of air =18 litres. 
Construction of plugs. — (a) Sugared glass-ivool. 
(b) Sugared glass-wool and sugar-powder. 
Colonies in flasks. — (a) 53 
(b) 3 
MDCCCLXXXVII.—P. 
T 
