318
A large amount may be given in half an hour with a continuous but slight effect upon the
several functions, but a mere fraction of this quantity given in half a minute may be suffi-
cient to cause death.
Now, variations in the effects of chloroform in any particular animal appear, in ordi-
nary circumstances, to be effected more powerfully by changes in the number and depth of
the respirations than by any other factor. When chloroform is given by inhalation in the
usual way (upon a cloth held near the mouth and nose), an amount of the drug which may be
used with safety during ordinary easy breathing may speedily produce dangerous results when
the respirations become rapid and deep. On some occasions I have tested this matter in a
slightly different way—by causing an animal to - breathe through the anæsthetic - bottle, and
o b s e r v i n g t h e i n f l u e n c e o f c e r t a i n d e f i n i t e d o s e s o f c h l o r o f o r m ( a ) d u r i n g e a s y b r e a t h i n g a n d ( b ) d u r i n g r a p i d g a s p i n g
r e s p i r a t i o n ,
t h e s t a t e o f t h e b l o o d - p r e s s u r e a n d t h eg
e n e r a l
c o n d i t i o n o f
the annual being similar in both instances. The chloroform was given by being introduced
into the anæsthetic bottle, through which the animal's (spontaneous) breathing was carried on.
The difference in the effects of a few minims of chloroform in the two cases was very striking;
a dose that had only a slight influence during easy breathing was productive of powerful effects
when given during rapid and deep respiration.
In experiments where artificial respiration was carried on by pumping air into the
lungs, I have often tested the same point. Respiration was first carried on at a moderately
slow rate (20 to 30 per minute), and the extent or depth of the respiratory movement was
such as to resemble easy breathing. A certain amount of chloroform was injected into the
anæs t het i c bot t l e, and i t s ef f ect s on t he bl ood- pr es s ur e, conj unct i val r ef l ex, et c. , r ecor ded.
When the results of this administration had passed away, a change was made in the artificial
respiration; the movements were accelerated (to 60 per minute), and rendered more extensive;
then chloroform in the same amount as before was introduced into the bottle. It was found
that equal doses of the anæsthetic, administered in the two different conditions of (a)
m o d e r - a t e r e s p i r a t i o n , a n d(
b )
exaggerated respiration, had remarkably different effects. With moder-
ate respiration, the results of a certain dose (for example, two minims), were very slight,
whereas the same dose during exaggerated respiration caused great depression—extensive fall
of blood-pressure, etc. In these thorax was intact, and the animal was unin-
jured save for the introduction of a canula into the carotid artery for the purpose of obtaining
a blood-pressure tracing, and a canula into the trachea for artificial respiration.
Similar results, were obtained in experiments conducted with thorax laid open and
recording apparatus applied to the heart, as described in Part II. of this Report. The minuteness
of the doses of chloroform required to produce very marked results in many of my experiments
(described in Part II.) was in close relation with the rapidity of the artificial respiration carried
on. Such a respiration was necessary in order to avoid the manifestation of spontaneous efforts
at breathing. Moreover, this rate is no greater than what is very frequently seen in the
spontaneous breathing of the cat under chloroform.
From the great variation in the influence of a definite amount of chloroform, according,
to the rate and depth of the respiration , it is evident that the ensuring of free dilution of