170 ON ANAESTHETICS 
the specific gravity of chloroform to the fluid measure employed. To take two 
illustrations from actual practice :—A tall, middle-aged man of pretty stout 
build was brought into a state of full anaesthesia in 4 minutes by means of 
1% fl. drachms of chloroform, or 138 grs.; 25 grs. would be about the quantity 
of chloroform remaining on a cap of the size used in his case, and if we allow 
450 cubic inches as the amount of air breathed per minute—and this is a mode- 
rate estimate—a calculation made as above indicated gives 4-9 as the percentage 
of chloroform by weight in the inspired air, or 1-17 by volume. Again, a woman, 
below the average stature and slightly built, was completely anaesthetized in 
44 minutes by means of 1} fl. drachms of chloroform, or 104 grs.: and supposing 
that 15 grs. remained on the considerably smaller cap used in her case, and 
that she breathed 300 cubic inches per minute, we obtain 5-2 as the percentage 
of the chloroform by weight, or 1-2 by volume. The mildness of these atmo- 
spheres will be apparent when I state that M. Paul Bert’s zone mamiable was, 
for the dog, from 7-3 to 15-3 per cent. by weight, or 1-7 to 3-5 by volume, and 
for the mouse, from 4:9 to 9-8 by weight, or 1-2 to 2:33 by volume, so that the 
atmospheres used in the two cases referred to were considerably below the zone 
mantable for the dog and only just at the lower limit of that for the mouse. 
Or the point will perhaps appear still more strikingly when it is borne in mind 
that 5 per cent. by volume was that which Dr. Snow employed with his inhaler, 
and 34 per cent. by volume that which was recommended as the average atmo- 
sphere by the chloroform committee of the Medico-Chirurgical Society... Even 
in the case of extremely shallow breathing, an atmosphere as strong as that 
recommended by the committee would probably never be reached by this method. 
Persons less amenable to chloroform than the average yield to these mild atmo- 
spheres if they are longer continued. Thus a lady who had often taken chloroform 
from the folded towel or compress, and had been with some difficulty brought 
under its influence, was subdued in the course of 7 minutes by means of 23 fl. 
drachms, or 207-5 grs., of chloroform. She was rather a large woman, and 
allowing that 20 grs. were required for moistening the towel, and that she 
breathed 400 cubic inches of air per minute, we find by calculation that the 
percentage of chloroform which she inhaled was 5-3 by weight, or 1-26 by volume. 
On another occasion, a somewhat larger cap being employed, she was anaes- 
thetized in 4 minutes with 2 fl. drachms, or 166 grs., of chloroform, giving a per- 
centage of 6-4 by weight, or 1-5 by volume. These are samples of several ad- 
ministrations in her case, and I observed that when the milder atmospheres 
were used she was free from the short fit of laboured and spasmodic breathing 
which invariably occurred when the larger cap with its stronger atmosphere 
* Vide Med.-Chir. Trans., vol. xlvii, p. 353. 
