ON THE CARBONIC ACID, ORGANIC MATTER, ETC., IN AIR. 
65 
The tripod employed was about three feet high, so that the samples were always 
collected at that height from the floor. 
As some adverse criticisms of Hesse’s method, contained in an article by 
Pawlowsky (‘Berliner Klinische Wochenschrift/ 1885, No. 21), appear to have 
attained some notice, it may be well to state that these criticisms, as will easily be 
seen on reading the article, depend on a complete misunderstanding of the method of 
sterilisation employed by Hesse. The new method suggested by Pawlowsky is not 
only no improvement, but would give absolutely nugatory results. 
We have preferred Hesse’s method on account of its great simplicity and other 
important advantages. We consider it to be a most convenient and elegant process. 
Miquel’s method (‘ Organismes Yivants de 1’ Atmosphere,’ p. 175) could not well have 
been applied by us under the conditions to which our work was subject. Miquel 
(p. 151) used as a standard nutrient medium a bouillon of Liebig’s extract, of 1'024 
specific gravity, and incubated it at 30° to 35°. How such a nutrient medium 
compares with Koch’s meat jelly, used under the conditions of our experiments, has 
not, so far as we know, as yet been determined. We cannot, therefore, compare at 
present the numerical results of our observations with those of Miquel in his valuable 
series of observations on the micro-organisms of outside air. 
In stating our results, the carbonic acid is represented in all cases by the number of 
the volumes of the gas contained in 10,000 volumes of air. 
The organic matter is represented by the volumes of oxygen required to oxidise the 
oxidisable organic matter in 1,000,000 volumes of air. 
The micro-organisms are represented by the number per litre of air. It must also 
be distinctly understood that this number includes only those which grow on Koch’s 
nutrient jelly of the composition previously stated, and kept in a room under ordinary 
conditions. If the jelly, for instance, were acid, the numbers and the ratio of bacteria 
to moulds would be different. 
Outside Air. 
In order to draw conclusions from an examination of air inside buildings, it is of 
course necessary to know the state of the outside air. As regards each of the con¬ 
stituents estimated, considerable variations were found, at different times and places. 
The following Table gives the results of determinations made on different days and 
in all kinds of weather during the winter and spring of 1885-86, and in various parts 
of the towns of Dundee and Perth. The observations were made at intervals over the 
same period as that during which the air of schools, houses, &c., was examined. 
MDCCCLXXXYII. —B. 
K 
