106 PROF. T. CARNELLEY, MR, J. S. HALDANE, AND DR. A. M. ANDERSON 
of carbonic acid and diminution of oxygen can easily be made up for by a slight increase 
in the rapidity of the respirations or flow of blood through the lungs, or in the depth 
of the former. We know also that there are many conditions, such as adherent pleurae 
or slight heart disease, which must have a very great influence on the function of 
respiration, and which yet do not appear seriously to affect the general health. 
The case of the oxidisable organic substances in air would appear to be totally 
different from that of the carbonic acid. These substances, unlike carbonic acid, 
appear to accumulate in stagnant air until they are present in quantities as large as, or 
even larger than, in pure expired air. Thus the average excess of the bleaching from 
expired air over that of the laboratory was found to be about 7'9 in the series of obser¬ 
vations detailed at p. 87, and the average excess in the ah of naturally ventilated 
schools was almost exactly the same. Although, as previously remarked, there are 
probably other factors to be taken into account here, the figures given are sufficiently 
striking. They make it appear probable that increased frequency of respiration may 
be of no avail whatever in making up for the impurity of the ah. 
The facts just alluded to appear all the more striking when we consider that expired 
air contains about 438 volumes per 10,000 of carbonic acid, whereas the highest 
carbonic acid found in schools was only 37’8 volumes. It is probable that poisoning 
by organic substances given off by the breath and skin has a very great effect in 
lowering the general health and predisposing to other diseases. The deaths from 
“ debility ” and “ convulsions ” in infants are perhaps in considerable proportions due 
to sub-acute poisoning by these substances. 
As regards the influence of the micro-organisms of air, it seems probable that for 
persons in perfect health the great majority of them are harmless. The ciliated 
epithelium of the respiratory passages probably sweeps them out as fast as they 
become entangled in the mucus with which it is bathed. Even those which have 
penetrated as far as the trachea and bronchial tubes are thus probably ultimately 
swallowed. It seems scarcely possible that any can ever reach the air-cells. 
The conditions are different, however, when there is even a slight catarrh of the 
respiratory passages. The bacteria in air are then probably a source of considerable 
danger. The bacteria doubtless propagate themselves in the secretions, which are 
only imperfectly expelled on account of the disorganization of the epithelium, and are 
therefore apt to be sucked or driven into the air-cells. A condition is thus pro¬ 
duced comparable in many respects to that in the deep part of a punctured wound. 
Broncho-pneumonia and further destructive changes seem a very natural conse¬ 
quence. It may be that few species of bacteria in addition to the bacillus of tubercle 
are capable of thus causing serious injury (see Thaon, ‘ Rev. de Medecine,’ December, 
1885), but that bacteria in ah do act in this way seems at least very probable. 
This hypothesis is quite in agreement with the death-rates given above. The 
enormous increase in the death-rate from acute bronchitis and broncho-pneumonia is due 
for the most part to a simple bronchitis (caused perhaps by exposure) becoming com¬ 
plicated with broncho-pneumonia, which latter runs an acute and rapidly fatal course. 
