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space of 500 cubic feet of air, and supply him with the same 
amount of air as he received in the small box, and it becomes 
rapidly noxious. We see, then, that the mode of supplying the 
air is one of the most important points. In a very small space 
a man may find a very little air to be enough by rapid venti- 
lation. In a considerable space a man may find himself un- 
comfortable from the want of ventilation, even although the 
amount of air supplied by ventilation is many times greater 
than in the small space.” No further quotation is necessary to 
show the nature of Dr. Smith’s views. The writer evidently be- 
lieves that in small spaces the heated air from the lungs ascends 
from the mouth, and is borne away by currents before it has had 
time to mingle intimately with the air of the chamber. This is, 
in fact, nothing less than a denial that thorough diffusion takes 
place. To accept Dr. Smith’s views, we must admit a partial 
diffusion only, and we fancy that the author’s system must admit 
draughts. Let us see, then, what Dr. Parkes has got to say in 
reply, for we could not state the argument against Dr. Smith 
in a more concise or intelligible form than it has been expressed 
by the distinguished Professor of Hygiene in the Army Medical 
School. Dr. Parkes first points out that the man in the box 
must not be supposed to draw in the air he requires from a 
supply-pipe, and to simply breathe it out by an exit- tube. If 
such were the case, the experiment would be equivalent to a man 
breathing in the open air ; but evidently this is not what Dr. 
Smith supposed. The man’s head being once more placed in 
the box. Dr. Parkes supplies him with 16 cubic feet of air for 
an hour, and he thus describes the result : “ At his first inspi- 
ration the man draws in 30 cubic inches of air from the box-air 
(which is at once replaced from outside), and then expels it, so 
that 30 cubic inches pass out of the box. These 30 cubic inches 
will be partly derived from the air of the box which has not 
gone into the lungs, and partly from the air from the lungs; con- 
sequently all the air from the lungs will not pass out , but some 
will remain in the box and render the air there slightly impure. 
... At the next inspiration 30 cubic inches are drawn into 
the lungs [the void being replaced from outside], and are then 
breathed out, and simultaneously 30 cubic inches of air pass 
out from the box. The 30 cubic inches which pass out are 
again made up of a mixture of the box-air and the lung-air. 
It is evident that the box-air must at every expiration become 
more and more impure, although at the end of the hour the 16 
cubic feet stated by Dr. Angus Smith to be sufficient will have 
been supplied.” We cannot afford space for further extract, 
but we may mention that Dr. Parkes makes a very simple 
arithmetical calculation of the quantity of carbonic acid accu- 
mulated in the box at the end of the hour, and shows most 
