ON THE CARBONIC ACID, ORGANIC MATTER, ETC., IN AIR. 
93 
to prevent condensation, A was surrounded by a cloth wrung out of hot water. As 
the heat would have melted ordinary jelly if used for B, Agar jelly was employed 
instead. Another similar apparatus was prepared and placed with its tube, E, close to 
the face of the first observer. A second observer inspired through the tube D of the 
second apparatus, expiring through his nose. Unrespired air was thus drawn into 
the tube B under conditions as nearly as possible the same as with the expired air of 
the first apparatus. 
Two pairs of experiments were first made when the laboratory was quiet. Each 
pair was carried out simultaneously, equal quantities of air being taken. The results 
were as follows :— 
^ f Respired air.0 
1 Unrespired air .... 1 mould 
^ J Respired air.0 
1 Unrespired air . . . . 1 mould. 
2 litres of air were aspirated in each case, the rate of aspiration being the same 
within a few seconds. 
It thus appears that micro-organisms are not given off in the ordinary respiration 
of healthy persons—or at least not to any appreciable extent. On the contrary, 
those present in the air appear to stick to the mucous membrane of the nose, larynx, 
trachea, &c., so that the air passages practically act as filters. In order to test this 
more thoroughly, we made another pair of observations, the laboratory being this time 
full of dust stirred up by vigorous sweeping, &c. Unfortunately, however, as will be' 
seen from the results of this experiment, the dust of this laboratory appears to 
contain very few micro-organisms. One litre of air was aspirated. The results were 
as follows :—• 
Respired ah-.0 
Unrespired air.3 bacteria. 
These results harmonise with Professor Tyndall’s demonstration of the optical 
purity of the last part of the air of each expiration. They are also in accordance 
with the whole of our experiments on vitiated air. Thus, by reference back to the 
Table (p. 86), it will be seen that, while the increase of carbonic acid runs parallel, on 
the whole, with the increase of organic matter, the micro-organisms first increase, and 
then diminish with the increase of carbonic acid. The latter diminution is also noticed 
if we take the rooms in the naturally ventilated Board schools, and divide them 
into three classes, according to the amount of carbonic acid. 
No. of cases. 
Micro-organisms. 
Class 1. (Carbonic Acid 7 - 88-15 - 77). 
12 
131 
„ 2. (Carbonic Acid 15-97-2078) . 
12 
235 
,, 3. (Carbonic Acid 21T4-37 - 84) . 
11 
84 
