[ 113 ] 
V. A New Method for the Quantitative Estimation of the Micro-organisms present in 
the Atmosphere. 
By Percy F. Frankland, Ph.D., B.Sc., F.C.S., F.I.C., Associate of the 
Royal School of Mines. 
Communicated by Professor Frankland, D.C.L., LL.D., M.D., F.R.S. 
Received November 15,—Read December 9, 1886. 
The quantitative estimation of the micro-organisms present in air is a problem which 
has attracted the attention of many experimenters since it received its first impetus 
at the hands of Pasteur “ twenty-six years ago. 
The method originally employed by Pasteur was of a very simple character, and 
consisted in preparing vacuous flasks of definite (j litre) capacity, each containing 
a small quantity of nutritive liquid ; the air in the flask was removed by boiling 
the liquid, and the open extremity was then sealed with the blowpipe. Such 
sealed flasks could then be preserved for an indefinite period of time without under¬ 
going change. By breaking off its sealed extremity, however, a certain volume of air 
rushes into the flask, carrying with it any microbes that it holds in suspension ; the 
flask is again immediately sealed, and if any microbes have gained access the liquid 
will, after suitable incubation, suffer visible alteration. On opening a number of such 
flasks in various places, Pasteur found that the proportion of them which suffered 
alteration was dependent upon the locality in which the experiment was performed. 
Thus, out of twenty such flasks exposed in the country at a distance from all habita¬ 
tions, eight became contaminated ; of twenty others exposed on the first heights of 
the Jura Mountains, five became infected ; whilst of twenty others exposed on the 
Montanvert (2000 metres high) one alone broke down. 
Tyndall, t in order to obtain an idea of the distribution of micro-organisms in the 
air, constructed a square table provided with 100 apertures, in which 100 test-tubes, 
each containing sterile culture-fluid, could be placed. This battery of tubes was then 
exposed to the air under examination, and the fate of the tubes watched from day to 
day. It was found that the tubes did not all suffer change simultaneously, but that 
the date of their alteration was dependent upon their position ; moreover, the changes 
taking place in the different tubes varied according to the particular kind of organism 
* ‘ Compt. Rend.’ vol. 51, 1860, p. 348. 
t ‘ Phil. Trans.,’ 1876, Part I. 
Q 
MDCCCLXXXVII.—B. 
1.0.87 
