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PROF. T. CARTEL LEY, MR. J. S. HALDANE, AND DR. A. M. ANDERSON 
and to different methods of ventilation, and other circumstances affecting the quality 
of the air. 
4'. An examination of the air in some other classes of buildings. 
5. An investigation into the sources of the organic matter and micro-organisms of 
air inside buildings, and the circumstances affecting the number of micro-organisms ; 
also of the relative number of bacteria and moulds in both outside and inside air. 
Methods. 
1. Carbonic Acid. — Pettenkofer’s well-known method was employed. 
2. Organic Matter. — The process described by Professor Carnelley and 
Mr. Mackie was made use of (‘Roy. Soc. Proc.,’ vol. 41, p. 23S). 
It must not be forgotten that the term “ organic matter ” is a very indefinite one, 
and that by it is really meant the bleaching action of the air on a dilute solution of 
potassium permanganate acidified with sulphuric acid. It therefore includes not only 
organic matter properly so called, but those substances which air sometimes contains, 
such as sulphuretted hydrogen, sulphurous acid, &c., which also bleach a permanganate 
solution. Even the organic matter itself may be of very different kinds and vary con¬ 
siderably as regards its influence upon health, some doubtless being quite harmless, 
whilst some may exert a very deadly effect. In so far, therefore, as the method does 
not distinguish between these various constituents of air, but brings them all into the 
same category, it is a very imperfect method. But, as no better process has yet 
been devised, it is the only one which has been at our disposal. 
3. Micro-Organisms .-—-In determining the number of micro-organisms, Hesse’s 
method (‘ Mittheilungen aus dem Kaiserlichen Gesundheitsamte,’ vol. 2, p. 182) was 
employed.* 
A piece of wide glass tubing, about 70 cm. long and 3'5 cm. wide, is closed at one 
end by means of a perforated india-rubber cork, through which passes a small piece of 
glass tubing about 10 cm. long and 1 cm. wide, and containing a plug of cotton 
wool at each end. The other end of the large tube is closed by two india-rubber caps 
fitting one over the top of the other, the inner one being perforated by a round 
opening of about 1 cm. in diameter. The whole being thoroughly cleansed, about 
50 c. c. of Koch’s jelly (containing the juice of 1 lb. of meat, 10 grammes of peptone, 
5 grammes of common salt, and 50-100 grammes of French leaf gelatine to 1 litre of 
water, and, after heating, very slightly over-neutralised with sodium carbonate) is 
introduced into the tube. The tube, with its contents, after replacement of the cork, 
is exposed to a temperature of 100 C., in an atmosphere of steam, for at least an hour, 
and then allowed to cool. When the jelly assumes a syrupy consistency the tube is 
* As Hesse’s method is not generally known, especially among chemists, and as the literature referring 
to it is not easily accessible, it has been thought advisable to describe it in greater detail than would 
otherwise be necessary. 
