ON ANAESTHETICS 141 
But, considering the great diffusibility of the vapour, and the large amount 
blown away in expiration, it is evident that only a small proportion of that 
which comes from the lower surface of the cloth really enters the lungs. Were 
it otherwise, it would be extremely dangerous to give chloroform with the cloth 
to infants, for as they inhale but a small amount of air, they would then breathe 
the vapour in a very concentrated state; yet all are agreed that infants are 
peculiarly favourable subjects for chloroform. In truth, the quantity dissipated 
into the surrounding air when the cloth is used involves considerable wastefulness 
in this means of administration, which is its only disadvantage as compared 
with an inhaler, but this is abundantly compensated by its greater simplicity, 
and consequent greater safety. For any apparatus which has the effect of pre- 
venting the free access of the atmosphere must be liable to operate in the same 
deadly manner as the bellows in the case above related, and even when con- 
structed upon the best principles, it will require most careful management, as 
is admitted by Dr. Snow with regard to his own inhaler.t. On the other hand, 
from the floor by a thread, connected with one end of the beam of a balance, projecting over the edge 
of the table on which it stood. The weight of the cloth having been ascertained, a weighed quantity 
of chloroform, corresponding to fl. 4jss., which is about the amount commonly used, was poured upon 
the middle of the lower surface of the cloth, which was then allowed to hang close above my face, so that 
I might breathe fully upon it, while inspiration was performed through a long india-rubber tube to avoid 
inhaling the chloroform vapour. The amount lost by the cloth was indicated by the weights in the scale 
at the other end of thebeam. At the commencement of an experiment the weight was made a few grains 
less than the sum of the weights of the cloth and chloroform together, and an assistant noted the second 
when the scale with the weights in it came to preponderate; then removed ten grains so as to allow the 
scale to rise, and again watched the time of its descent ; and repeated this process several times, thus 
obtaining a very accurate record of the rate of alteration in the weight. The lower surface of the cloth, 
which was made slightly concave, was circumstanced just as in the early period of the administration 
of chloroform, except that the inspired air was drawn from a distance. Inspiration does not, however, 
materially affect the rate of evaporation, as was found by experimenting with a cloth arranged above 
the mouth of a tube into which air was drawn by an appropriate apparatus. Allowance being made 
for the slight gain in weight that the cloth would obtain from absorbing moisture from the breath, 
the amount of chloroform lost from both surfaces together was thus easily determined. In order to 
ascertain how much escaped from the upper surface, experiments were made with the same cloth, having 
first the upper and then the under side securely covered with oil-silk, the arrangements being as above 
described, except that my face was not below the cloth. The quantity given off from the upper surface 
in a normal atmosphere was thus determined; and this being subtracted from the whole loss from 
both surfaces under the circumstances of inhalation, gave the amount that evaporated from the lower 
surface only. Atthe temperature of 70° Fahr. this proved to be, from the average of several experiments, 
at about the rate of 24 grains per minute during the first half-minute ; and allowing, with Dr. Snow, 
that 20 grains of chloroform correspond to 15-3 cubic inches of the vapour, and that 400 cubic inches 
of air are inhaled in a minute, we get 4:5 per cent. as the proportion of the chloroform to the inspired 
air, on the hypothesis that all that evaporates from the lower surface enters the lungs; 5 per cent. 
being what Dr. Snow was led by his experiments to regard as the proportion at which the respiration 
was quite sure to fail before the circulation, and that at which he aimed with his inhaler (op. cit., p. 34). 
On the other hand, Dr. Snow assumed that, when the cloth is used at a temperature of 70° Fahr., 
9:5 per cent. of chloroform is really inhaled (op. cit., p. 34) ; whereas, in truth, of the 4-5 per cent. a large 
amount is dissipated into the surrounding air. 
+ Op..CIt.. pp. Tél, 188. 
