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amount without producing any striking effect; the chloroform may be pushed, and then when
the pressure suddenly rises dangerous effects may speedily ensue if the administration of the
anæsthetic is continued in the same way (in the same strength) as was employed during the
state of low pressure; the amount of chloroform reaching the vital organs becomes much
augmented with a high pressure. It is evident, then, that a low blood-pressure must last for
some time, so as to lead to a more abundant administration of chloroform, before any danger can,
with reasonable care, be caused by a change to a higher pressure. Hence the occurrence of a
very brief and transient phase of low pressure (such as may be caused by a short inhibition of
the heart), followed by a speedy rise to the normal height, does not introduce any special
danger in the use of chloroform; for the period of low pressure does not last long enough to
induce the administrator to give chloroform more abundantly, and thus there no danger in
t h e s u b s e q u e n t r i s e .
Apart from the influence of asphyxial conditions, a change from a ve ry low pressure to
high pressure is very rare under chloroform. Such a change can, of course, be easily
b r o u g h t i n t e n t i o n a l l y ( f o r e x a m p l e , b y s t i m u l a t i o n o f t h e v a g u s , c o m p r e s s i o n o f t h e v e n a c a v a
inferior, etc.), and it may possibly occur in certain peculiar circumstances of operative proce-
dure, but its occurrence in such a degree as to constitute a serious danger in chloroform
administration is probably rare
.
On the other hand, it has been already stated that during imperfect anæsthes
ia a sudden change from a moderate to a high pressure (caused by sensory irritation) may co-operate
with exaggerated respiration in leading to the intake of a dangerous overdose.
Indication of Danger during Chloroform Administration dericable from the Respiration
and from the Blood-pressure.— The relative importance of observation of the respiration and
the blood-pressure with regard to the warnings of danger derivable from them was studied
in many experiments in the following manner: A cat rendered unconscious with chloroform in
the usual way, was fastened on a Czemark's holder; a blood-pressure tracing was taken
(by means of a Ludwig's kymograph) from the carotid artery, and a tracing of the respiration
by a tambour kept in contact with the animal's chest and communicating with a recording tambour
which inscribed its movement on the recording surface simultaneously with the blood-pressu
re tracing. More chloroform was then given on a cloth held near the animal's mouth and nose,
and after a time the anæsthetic was pushed. The course of the blood-pressure
and the respira-tion was accurately registered by their tracings; it was found that indications of approaching
danger were given most commonly by the respiration, but this was by no means inrariably the
case. In several instances warning was given first by the blood-pressure. A sudden and
precipitous fall of pressure occurred at varying periods—fifteen, twenty-five, thirty seconds,
and even longer—before there was anything in the state of the respiration to cause alar
m , a n d e v e n t h e n t h e r e s p i r a t i o n d i d n o t s t o p , b u t b e c a m e s l o w e d a n d s o m e w h a t s p a s m o d i c i n i t s
character. Sometimes a slight change either in rate or force is seen in the respiratory tracing
along with, or very soon after, the fall of pressure, but such a change would not have been
apparent to the eye without the use of accurate recording apparatus: and even when
v i s i b l e t o t h e e y e , t h e r e s p i r a t o r y c h a n g e s a c c o m p a n y i n g a d a n g e r o u s f a l l o f p r e s s u r e w e r e s o m e t i m e s
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