ON THE CARBONIC ACID, ORGANIC MATTER, ETC., IN AIR. 
105 
observation, whereas the number of micro-organisms is largely dependent on its 
previous history, as shown above. 
(5.) In proposing the above standards, we wish it to be distinctly understood that 
they should be taken in conjunction, and not singly. The carbonic acid, more 
especially, is not a safe guide when taken alone. 
(6.) The standard for micro-organisms is for Koch’s jelly, of the composition 
previously stated. 
So far as we are aware, a standard of purity has not previously been proposed for 
organic matter and micro-organisms. 
The Nature of the Micro-organisms present in “Vitiated Air.” 
On this point we purpose to say but little at present. The great majority of the 
colonies which appear on the jelly consist of micrococci of very various kinds and with 
various naked-eye appearances (see Plate 6, figs. 2 and 3). Bacilli are not nearly so 
common; the moulds are also of very various kinds. As was to be expected, these colonies 
are not always pure cultivations. In conjunction with Dr. Hare, of the Surgical 
Laboratory, Edinburgh University, one of us has cultivated and described some of the 
more characteristic and commonly occurring species. A series of inoculation and 
inhalation experiments with pure cultivations was also begun under Dr. Hare’s 
direction in the same laboratory. The results of these experiments were negative in 
the case of the few species tried as yet. 
Probable Influence on Health of the different abnormal Constituents 
of Vitiated Air. 
We have placed (p. 74) the results of our analyses alongside of statistics as to the 
death-rates in the classes of houses the air of which we examined; but it is no very 
easy task to determine how far differences in the death-rate are due to differences in 
the air breathed, and how far to other causes, such as improper or insufficient food. 
There is, however, abundant evidence from other sources as to the enormous influence 
on the death-rate of the air habitually breathed, apart from other causes (cf. Parkes’ 
‘Hygiene,’ 6th edn., p. 133). Hence we may take it as quite certain that the above 
differences in the death-rates in Dundee are largely due to the differences in the 
quality of the air habitually breathed. 
As regards the influence of the separate constituents by which the air was contami¬ 
nated, it is even more difficult to come to positive conclusions. # But a short discussion 
as to what seems probable may serve at least to give a more definite direction to one’s 
ideas in considering the matter. 
As regards carbonic acid, it seems almost certain that its presence in houses in the 
proportions we found could not have a sensibly deleterious effect. A slight increase 
* We hope to throw further light on this point by a series of direct experiments on animals with air 
containing vitiating constituents separately, and not in such proportions as to cause acute poisoning. 
MDCCCLXXXVII.—B. P 
