124 DR. P. F. FRANKLAND ON THE QUANTITATIVE ESTIMATION OF 
Plug mixed with 20 c.c. of sterilised water, 1 c.c. of which gave on plate- 
cultivation :— 
Colonies, 26, 21, 21 . . . Average = 22‘7 colonies. 
Plate similarly prepared from control- 
plug gave colonies 6, 3 . Average = 5 ,, 
119 litres of air yielded .’. 177 X 20 = 354 ,, 
10 „ „ 30 
No. 2. Afternoon. Heavy shower since morning. 
Volume of air aspirated = 119 litres. 
Construction of plug .— Similar to above. 
Rate .—8 strokes per minute. 
Plug mixed with 20 c.c. of sterilised water, 1 c.c. of which gave on plate- 
cultivation :— 
Colonies, 4, 12, 9 . . . Average = 8'3 colonies. 
Plates similarly prepared from control - 
plug gave colonies 1, 0 . Average =1 ,, 
119 litres of air yielded .*. 7'3 X 20 = 146 ,, 
10 „ „ 12 
X. Roof of Science Schools. July 29, 1886. Wind, S. by S.W., gentle. No previous 
rain. Roads watered. 21 0- 3 C. 
No. 1. Morning. Volume of air aspirated =119 litres. 
Construction of 'plug. —Glass-wool and glass-powder. 
Rate .—8 strokes per minute. 
Plug mixed with 20 c.c. of sterilised water, 1 c.c. of which gave on plate- 
cultivation :— 
Colonies, 28, 19, 16 . . . Average = 21 colonies. 
Plates similarly prepared from control- 
plug gave colonies 5, 4 . Average = 4'5 ,, 
119 litres of air yielded .\ 16'5 X 20 = 330 „ 
10 „ „ 28 
No. 2. Afternoon. Volume of air aspirated =60 litres. 
Construction of plug .—Same as No. 1, more closely packed. 
Rate .—4 strokes per minute. 
Plug mixed with 10 c.c. of sterilised distilled water, of which 1 c.c. gave on plate- 
cultivation :— 
Colonies, 19, 27, 21, 24 . Average = 22*8 colonies. 
Control-plates of No. 1 must be 
applied to No. 2, viz., 4\5 colonies 
60 litres of air yielded 18 , 3xl0=183 ,, 
10 „ „ 31 
