1886.] The Distribution of Micro-organisms in Air. 523 



At the suggestion of Mr. Edwin Chadwick, C.B., I was induced to 

 make a comparison between the air at different altitudes in towns. 

 The results obtained are recorded in the above table. 



These figures are particularly instructive, as illustrating the fact 

 that with increasing altitude the air becomes poorer in micro-organ- 

 isms. The tube experiment on the Golden Gallery at St. Paul's on 

 the 29th May must be disregarded, as during the progress of the 

 experiment the direction of the wind changed completely and vitiated 

 the result by blowing down the open extremity of the tube, thereby 

 increasing the number of organisms deposited beyond, what was 

 actually due to the volume of air aspirated. The exposed dish, on 

 the other hand, would not be affected in the same way, and it will be 

 seen that, as regards the number of organisms falling on the square 

 foot, the result on the Golden Gallery carries on the diminution 

 noticed on the Stone Gallery. 



The differences noticed in the case of the St. Paul's experiments 

 may perhaps be most vividly appreciated by comparing the averages 

 of the two experiments with some of the averages already quoted for 

 other places. Thus at the base of St. Paul's we find an average of 

 56 organisms in 10 litres, which is considerably greater than the 

 average for the South Kensington experiments, in which only 35 were 

 found in the same volume ; on the Stone Gallery there were 29 in 

 10 litres, whilst in the Golden Gallery in the successful experiment 

 the number only amounted to 11 in 10 litres, thus closely resembling 

 the average number found in the experiments made in country places, 

 which was 14 in that volume. 



