[Vor. 1 
48 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
The proportion of carbon dioxide is still the standard mainly 
relied on for estimating pollution of air by materials given off 
from the human body, although it is recognized that other 
factors may be of more importance. This method of exam- 
ining air, however, is of little or no value in furnishing an index 
to the probable or possible contamination with disease-pro- 
ducing germs, for there is at present no reason for believing 
that such organisms are given off in the breath during ordinary 
quiet breathing. Thus, M. Н. Gordon! calls attention to the 
following: Tyndall observed that expired air is optically purer 
than inspired air; Cornet found air expired by tubercular patients 
to be free from the tubercle bacillus; and Straus has shown that 
expired air is not only comparatively free from bacteria, but 
that it is considerably purer in this respect that inspired air. 
It nevertheless appears probable that bacteriology rather than 
chemistry will furnish à means of investigating the pollution 
of air by disease-producing germs. Тһе problem at hand is 
to devise, if possible, а method for estimating the degree of 
pollution of air by pathogenie organisms (given off from the 
human body) in a manner similar to that employed in estimat- 
ing the extent of pollution of water by similar organisms of 
excrementa] origin. 
HISTORICAL 
It appears that the present status of bacteriological analysis 
of air is comparable to that of bacteriological analysis of water 
some years ago, when the total number of bacteria in a given 
quantity was the chief factor determined. There are various 
ways in which pathogenic organisms may gain access to the 
air and ultimately to another individual. In addition to trans- 
fer by direct contact, disease-producing organisms may be given 
off in the urine, in feces, in sputum, or from the surface of the 
skin. Recently, also, attention has been called to the possi- 
bility of the pollution of air by the scattering of fine particles 
of mucus and saliva from the mouth in the acts of coughing, 
sneezing, and loud speaking. The latter methods of air pollu- 
1 Report on a bacterial test for estimating pollution of air. Supplement to the 
Thirty-second Annual Report of the Local Government Board (London), containing 
the Report of the Medical Officer for 1902-3. 421-471. 1904. 
