140 
June, 1889. 
president’s address. 
From the Hall of St. Christopher ... ... 6,300 
From the Ward of an Hospital ... ... ... 11,000 
But of these only one in ten was alive and capable of develop¬ 
ment ; the rest were dead. 
This is at the surface of the earth, not far above sea-level. 
The higher we go the fewer the Bacteria become ; and at an 
elevation of about 7,000 feet they have entirely disappeared. 
No Bacterium or Fungus spore of any kind was detected at 
that height. On the surface of glaciers, too, they are nearly 
absent. The number found in any given locality varies, of 
course, with circumstances. Immediately after rain, the 
air, which has been, so to speak, washed, contains fewer than 
at other times. They also vary with the seasons. In the 
same park at Montsouris, Miquel found 49 per cubic metre 
in the winter, 85 in the spring, 105 in the summer, and 142 
or even more in the autumn. This has been confirmed bv 
%/ 
Frankland, and thus the common belief in the greater 
impurity and unhealthiness of the atmosphere in the latter 
season has been justified. It is easy also to see why it should 
be so, for autumn is the season when the greatest amount of 
vegetable putrefaction is going on, and when the opportunities 
for the increase of putrefactive Bacteria are the greatest. 
But there is another consideration which influences more 
effectively the number of Bacteria present in the air of an 
enclosed space, and that is the presence or absence of atmo¬ 
spheric currents. Even the smallest germ has weight, and in 
perfectly still air will fall to the ground. It is found that 
if the manipulation of the sterilised gelatine takes place 
in a room where the air is in motion, or where the fallen 
Bacteria have recently been disturbed by sweeping or dusting, 
contamination is inevitable, but if all doors and windows be 
securely fastened, and all the movements be performed quickly, 
but steadily, then no contamination arises unless the number 
of germs in the room is enormously great. As an instance 
of the latter, Dr. Klein records that, after a large number 
of experiments had been performed in his laboratory with 
Bacillus anthracis, the air became so full of the spores of that 
species that they introduced themselves unbidden into every 
cultivation. 
Dr. Frankland showed how the quantity of floating 
Bacteria present can be measured by the number which falls 
upon a square foot of horizontal surface per minute. The 
average at Kensington was 279 per square foot; but on a cold 
windy day 433 fell per minute. In the country 79 fell per 
minute; in Hyde Park 85. In enclosed spaces, such as rooms, 
the number was much smaller, but the effect of agitation of 
