94 
PROF. T. CARNELLEY, MR. J. S. HALDANE, AND DR. A. M. ANDERSON 
The lower number of micro-organisms with a higher amount of carbonic acid may 
probably be due to the filtration of the air through the air-passages of the scholars 
—not a very desirable process of purification. 
A similar Table for 1- and 2-roomed houses does not show this diminution, but could 
not have been expected to do so, considering the small amount of carbonic acid as 
compared with schools. The rooms, when divided into equal classes, according as the 
carbonic acid was above or below a middle point, give the following results :— 
Micro- organism s. 
One-roomed • 
Carbonic acid above. 
Carbonic acid below . 
76 
57 
Two-roomed • 
' Carbonic acid above . 
38-5 
_ Carbonic acid below . 
38T 
Some experiments in the Chemical Lecture-rooms will be of interest in this con¬ 
nexion. At a popular lecture, during which the Large Lecture-room was crowded, and 
the ventilating apparatus was not in action, the carbonic acid and organic matter were, 
after an hour, 37'61 and 15'8 respectively (average of two determinations each). The 
micro-organisms, at the same time, were only 6 per litre. Again, in the Small Lecture- 
room (ventilation closed), just before the entry of the students (carbonic acid 5'18, 
organic matter 4'8), 2'5 micro-organisms per litre were found, while at the end of the 
lecture (carbonic acid 19'57, organic matter 11'2) 1'5 per litre were found. In another 
experiment in the same room (ventilation open) 3 micro-organisms per litre were 
found at the beginning (carbonic acid 3'46, organic matter 9 - 2), while 1*5 were found 
at the end (carbonic acid 13'21, organic matter 13'1). 
2. The skin and clothes of the persons present in a room at the time of an 
observation also occur naturally as a probable source of infection of air. That this 
source, however, is of much less importance than might be supposed may, we think, 
be shown from our observations. 
In order to obtain data on this point, it is necessary to eliminate as far as possible 
disturbing influences arising from the condition of the room itself, particularly, as will 
be seen from the sequel, habitual bad ventilation and want of cleanliness. The 
Chemical Lecture - rooms are habitually ventilated mechanically, and frequently 
scrubbed ; hence the experiments made in them are of special value in this reference. 
The observations in the large room were made during a course of evening popular 
lectures on political economy, the audience being drawn from various classes of 
society. There was occasional applause, which must, of course, have tended to stir 
up micro-organisms. The following were the results :— 
