140 ON ANAESTHETICS 
nected with a tube tied into the trachea, the animal having been previously 
put under the influence of chloroform. The chest having been opened, the 
investigation was continued for a while, when the creature began to exhibit signs 
of returning consciousness. To avert this I removed the bellows, and poured 
into them a considerable quantity of chloroform, and resumed the artificial 
respiration with energy for a short time, the natural respiratory movements 
meanwhile continuing ; when suddenly the heart, which lay exposed before us, 
ceased to beat, and refused to contract again even when its muscular substance 
was pinched, which showed that its nervous apparatus was paralysed. 
This was no doubt caused by the air becoming highly charged with chloro- 
form in passing over the extensive evaporating surface presented by the interior 
of the bellows. For it had been before shown by Dr. Snow, from experiments 
upon the lower animals, that an atmosphere containing more than a certain 
percentage of the narcotic vapour stops the heart before breathing ceases, 
whereas the reverse occurs when the chloroform is more diluted with air.! 
Hence, with the view of preventing fatal syncope, Dr. Snow contrived an inhaler 
for regulating the amount of chloroform vapour in the inspired air, and used 
it in upwards of four thousand cases, of which only one was fatal, and even 
that seemed to be so independently of the chloroform. Finding his ingenious 
efforts crowned with such success, and charitably supposing that all were as 
careful as himself, he concluded that fatal cases in the hands of others could 
result only from a faulty method of administration ; and assuming that when 
chloroform is given from a folded cloth it is apt to be in too concentrated a form, 
he attributed most of the deaths that have occurred to paralysis of the heart 
from this cause. | 
But the cloth being the means which has been used from the first in Edin- 
burgh, with success even superior to Dr. Snow’s, I have been long satisfied 
that his argument was fallacious; yet as his special devotion to the subject, 
and the valuable facts which he has communicated regarding it, render his 
opinion influential, I have thought it worth while to subject a matter of such 
great practical importance to experimental inquiry; and, about the usual 
quantity of the liquid being employed, I find that, so far from the amount of 
chloroform given off from the cloth being in dangerous proportion to the air 
inhaled, the whole quantity which evaporates from the under surface, even 
when the rate is most rapid, viz. just after the liquid has been poured upon it, 
is below Dr. Snow’s limit of perfect security against primary failure of the heart.” 
* I have noticed, however, that different animals differ in their susceptibility to chloroform. Thus 
frogs or mice may be kept for any length of time under its influence ; but bats are very apt to die when 
treated in exactly the same way. 
* The experiments were performed in the following manner: A cloth, similar in all respects to what 
would be used in practice, was supported upon a light wire framework, and suspended at a little distance 
