THE MICRO-ORGANISMS PRESENT IN THE ATMOSPHERE. 
125 
XT. Roof of Science Schools. July 31, 1886. Afternoon. Wind, N.W., variable in 
strength. Showers previous to and during experiment, also rain during previous 
night; the outside of the tubes was wetted by rain. 20° C. 
Volume of air aspirated = 119 litres. 
Construction of plug. —Glass-wool and glass-powder. 
Rate. —4 - 8 strokes per minute. 
Plug mixed with 20 c.c. of sterilised water, 1 c.c. of which gave on plate- 
cultivation :— 
Colonies, 24, 22, 26 . . . Average = 24 colonies. 
Plates similarly prepared from control- 
plug gave colonies 10, 8 . Average = 9 ,, 
119 litres of air yielded .\ 15 x 20 = 300 ,, 
10 „ ,, 25 ,, 
XTT. Roof of Science Schools (west side). August 4, 1886. Morning. Wind, N.W. 
by N. and very gentle, no rain on previous day or night. 17°'2 C. Roads well 
watered. 
No. 1. Volume of air aspirated = 60 litres. 
Construction of plug .—Sugared glass-wool and sugar-powder. 
Rate. —3'2 strokes per minute. 
Plug mixed with 10 c.c. of sterilised water, 1 c.c. of which gave on plate- 
cultivation :— 
Colonies, 31, 27, 24 . . . Average = 27'3 colonies. 
Plates similarly prepared from control- 
plug gave colonies 5, 3 . Average =4 ,, 
60 litres of air yielded .'. 23‘3 X 10 = 233 „ 
10 „ „ 39 
No. 2. Volume of car aspirated = 60 litres. 
Construction of plug .—Sugared glass-wool and sugar-powder. 
Rate. —3'4 strokes per minute. 
Plug mixed with 10 c.c. of sterilised water, 1 c.c. of which gave on plate- 
cultivation :— 
Colonies, 32, 28, 30 . . . Average = 30 colonies. 
Control-plates of No. 1 must be applied 
also to this. 
60 litres of air yielded 26X10 = 260 ,, 
10 „ „ 43 „ 
XIII. Roof of Science Schools (east side). August 4, 1886. Afternoon. Wind, 
E. to S.E., stronger than in morning. 
Volume of air aspirated =48 litres. 
Construction of plug .—Sugared glass-wool and sugar-powder. 
