VENTILATION AND VENTILATORS. 
405 
conclusively that long before this time the man would commence 
to be poisoned with his carbonic acid alone, to cc say nothing of 
the organic matter evolved from his lungs. 
It seems to us that in all respects Dr. Parkes’ explanation of 
the state of things in the supposititious case selected by Dr. 
Smith, is in accordance with theory and experience. However 
much we may be disposed to admit that complete diffusion does 
not occur, we cannot deny that there is considerable admixture 
of the gases, and this is adequate to bring in a verdict for Dr. 
Parkes. We see, then, that in calculating the quantity of air 
to be supplied to an individual, we must not be guided alone 
by the number of cubic feet of pure air consumed per 
hour. We must take diffusion into account. The proposition 
may be fairly laid down, however startling it may appear, that 
in order to make the conditions of respiration in a room as 
healthy as they are in the open air, the whole air of the room 
should be renewed at each respiration . Put this would not be 
possible, for in order to do so, we should have to produce a 
series of air-currents which would be perfectly intolerable. Our 
object, then, must be to prevent the vitiation of the air beyond 
a point which can be borne without injury to health. In the 
air which we breathe out of doors, we find that there is *4 
part of carbonic acid in 1000 parts; and we know from expe- 
rience that an atmosphere which contains *6 per 1000 of carbonic 
acid may be breathed with impunity. Our aim, then, must be — 
admitting diffusion — to supply such a quantity of air per hour 
as will keep down the pollution of the air to this standard. 
Here, again, arises the question, Can this be effected more easily 
in a small room than in a large one ? This is a problem of some 
gravity ; and, in our opinion, its only correct solution is that 
given by a mathematician — Professor Donkin, F.R.S. On this 
point we differ from both Dr. Smith and Professor Parkes. The 
former would, of course, allege that the smaller space is the more 
convenient ; the latter contends that a larger apartment is more 
easily ventilated. According as we view the matter from dif- 
ferent standpoints, each is right, though both, in our opinion, 
are in some respects in error. In a small room, with a very 
powerful out-draught, the quantity of air demanded per minute 
might be smaller than that demanded for a larger one. Again, 
in a large room we have the advantage of a large supply of air 
to dilute the poisonous gas. A little reflection, however, will 
show that in both cases, unless the increasing impurity be kept 
under, the rooms will, at a certain period, become uninhabitable. 
This, we think, is a point which has been overlooked by Dr. 
Parkes. Those who read Professor Donkin’s observations on 
the subject can decide whether we are right or not ; but we con- 
fess that we cannot see what the size of the room has to do 
