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the anæsthetic bottle, through the same channel traversed by the air passing into the lungs
when artificial respiration was used. Chloroform could readily be added (by means of the
hypodermic syringe) to the air as it passed through the bottle: and thus definite doses of the
anæsthetic could be administered to the animal, inhaled by its own spontaneous respiratory
movements. The effects of accurately measured amounts of chloroform (given in this way)
upon the blood-pressure, the conjunctival reflex, and the general condition of the animal were
carefully recorded. Then, after an interval, when the effects had been recovered from, artificial
respiration was substituted for the spontaneous breathing, the other conditions of the experi
- m e n t r e m a i n i n g u n c h a n g e d ; a i r w a s p u m p e d t h r o u g h t h e a n æ s t h e t i c b o t t l e i n t o t h e l u n g s ,
instead of being inspired in the ordinary way; an equal dose of chloroform was administered
and its effect watched. The influence of the anæsthetic was found to be remarkably similar to
what was seen during spontaneous inhalation, provided the rate and depth of the artificial
respiratory movements were made to correspond with the rate and depth of the spontaneous
respirations. Two or three minims of chloroform induced similar effects, as evidenced by the
blood-pressure, the conjunctival reflex, and the general condition, whether the chloroform vapour
was taken in by the spontaneous breathing of the animal or was artificially pumped into the lungs.
Hence it may be concluded that the intake of chloroform is substantially the same whether it
is given by spontaneous inhalation (in which case the pressure within the lungs during the
inspiratory movement is negative), or by artificial respiration, when the pressure within the
lungs during the phase corresponding inspiration is positive. The abnormal conditions
of artificial respiration do not apparently make any essential difference in regard to the effects
of chloroform, provided the number and depth of the respiratory movements are the same, and
the percentage of chloroform in the air taken into the lungs is identical in the two cases.
4. The nature and extent of the fall of blood-pressure caused by chloroform is, as a rule,
an excellent guide to the degree in which the influence of the drug has been exerted upon the
general condition of the animal. When the fall is sudden and extensive it gives ground for
a p p r e h e n s i o n t h a t a n o v e r d o s e h a s b e e n a d m i n i s t e r e d ; o n t h e o t h e r h a n d , w h e n t h e f a l l s i s g r a d u a l a n d m o d e r a t e
we many s af el y as s ume t hat t he amount of chl or of or m i n t he ci r cul at i on
is not too great. Now, applying this test to the experiments described in Part II., we find that
dilatation of the heart is present when the fall of pressure is no greater or more sudden than
often occurs—without arrest of the respiration or other serious result—when an animal (with
intact thorax) inhales chloroform in the ordinary way. For example in an animal taking
chloroform by natural respiration the blood-pressure—as shown by a kymograph connected
with the left carotid artery—was reduced by chloroform from 160 millimêtres to 80 millimêtres
and again from 160 millimêtres to 94 millimêtres, without stopping the respiration. In the same
animal after the thorax had been opened and the cardiac recording apparatus applied, a much
slighter reduction of pressure by chloroform—from 112 millimêtres to 94 millimêtres—was
accompanied by pronounced dilatation of the heart. Moreover, in one instance, chloroform
caused distinct dilatation while the pressure remained tolerably steady at about 1
0 6 m i l l i m ê t r e s . S u c h r e s u l t s s h o w c l e a r l y t h a t c a r d i a c d i l a t a t i o n m a y o c c u r a t a t i m e w h e n t h e a m o u n t o f
chloroform in the circulation is not excessive—when there is reason to believe that the anæs
-thetic is present in no larger amount than during ordinary inhalation.
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