311
raising the pressure. But by far the most powerful means of influencing the carotid pressure
under chloroform is by applying continuous firm pressure over the intact abdomen or to the
abdominal aorta directly. In this way, unless the heart has been directly paralysed by chloro
-form, a well-marked rise of blood-pressure can be brought about in the carotid and other arteries
of the upper part of the body (head, neck and chest), and the circulation in that, part is
greatly improved in rate and volume. This method of causing a rise of pressure under chloro
-form has been very frequently tested in the course of my experiments, and is strikingly illus
-trated in the tracings I have taken. Even when chloroform has been given in an amount
sufficient to cause stoppage of the respiration and a formidable fall of blood-pressure, the
immediate application of firm pressure over the abdomen or compression of the abdominal aorta
has, as a rule, caused a rise of pressure. At the moment of respiratory failure, the heart,
though dilated, is, as a rule, capable of acting with some effect, but it soon becomes fatally
incapacitated in consequence of the influence exerted upon the already-depressed cardiac me
-chanism by respiratory and vascular failure; the interference with the nutrition of the heart
substance resulting from arrest of the breathing, or dependent on
excessive and continued
fall of the blood-pressure, even apart from stoppage of the respiration, must necessarily
exart a rapidly destructive influence on the activity of an already embarrassed and depressed
organ. At the time the respiration stops, the heart is usually (though not always) able to act
in a way sufficient to maintain a certain amount of blood-pressure, compatible with the con
-tinuance of life, provided the vaso motor system is not paralysed. The heart then being, in the
majority of cases, still able to exercise its function to some purpose, it is easy to understand
that a great increase in the peripheral resistance should be attended by a rise in the arterial
pressure, the amount of the rise varying largely according to the power still possessed by the
heart. The application of firm pressure over the intact abdomen causes, in addition to an in
-crease in the peripheral resistance of the arterial system, the propulsion of a considerable amount
of blood from the vessels of the abdominal cavity through the vena cava inferior into the heart.
Compression of the aorta by itself causes a great rise of pressure; this shows that a large i
n-crease of the peripheral resistance, even apart from the forcing of more blood into the right side
of the heart, is sufficient to cause all extensive rise of pressure.
PART III
R e l a t i o n o f t h e R e s u l t s d e s c r i b e d a b o v e t o w h a t o c c u r s d u r i n g t h e I n h a l a t i o n o f C h l o r o f o r m
i n t h e I n c e n t A n i m a l . —
H o w
f a r a r e t h e s e r e s u l t s a p p l i c a b l e t o t h e i n t a c t a n i m a l i n h a l i n g c h l o r o f o r m i n t h e o r d i n a r y w a y ? I t
is of course obvious that in certain respects the conditions
of experimentation above described are widely different from what obtain when an u n i n j u r e d
animal takes in chloroform by its natural respiratory movements in the ordinary way.
I n t h o s e t h e t h o r a x l a i d o p e n r e n d e r i n g s p o n t a n e o u s b r e a t h i n g i m p o s s i b l e ,
and artificial respiration by pumping air into the lungs was substituted. With artificial respira-
tion of this kind, although the amount of air and the percentage of chloroform entering the
pulmonary air cells may be the same as in natural breathing, still there is a certain difference
t o b e c o n s i d e r e d , n a m e l y , t h a t w h e n a i r i s p u m p e d i n t o t h e l u n g s t h e p r e s s u r e w i t h i n t h e l u n g s
is a positive pressure during the phase corresponding to inspiration (that is, when the lungs are
inflated with air); whereas, during the inspiration of air in natural breathing the pressure