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5. Evidence of great importance in regard to the question under consideration is
afforded by the state of the conjunctival reflex.* We have seen that pronounced changes may
occur in the heart before the conjunctival reflex is completely abolished. This shows plainly
that the amount of chloroform in the circulation was not excessive, else the reflex would not
have been present. We know that the conjunctival reflex is, as a rule, abolished long before
there is any danger of respiratory paralysis. The presence of the conjunctival reflex during
cardiac dilatation makes it plain that a comparatively small amount of chloroform—less, indeed,
than is commonly used for deep anæsthesia—can affect the condition of the heart in a notable
degree. There could hardly be a stronger proof. The abnormal condition of the experiment can
scarcely interfere with the abolition of the conjunctival reflex at least not more than operative
procedure of various sorts. Further, it is clear that, as a comparative test of the action of
chloroform and ether, the presence of the conjunctival reflex is of prime importance. Any in-
fluence exerted by abnormal conditions of experiment is present equally in both cases; hence
they cannot interfere with the fair comparison of the two anæsthetics.
6. Another form of experiment may be brought to bear upon the question under
consideration. A cat is deeply chloroformed by natural inhalation in the ordinary way, by
holding a cloth with a small quantity of chloroform near the animal's mouth and nose. Deep
anæsthesia is brought about, the conjunctival reflex being completel
y abolished, while the respi-ration goes on regularly. Then the chest is rapidly opened and the heart examined. In so
m e c a s e s I h a v e c a u s e d a r t i f i c i a l r e s p i r a t i o n — b y m e a n s o f a c a n u l a t h r u s t i n t o t h e t r a c h e a — t o b e
performed as soon as I began to open the chest, in order to avoid any chance of error from
a n a s p h y x i a l c o n d i t i o n b e i n g d e v e l o p e d d u r i n g t h e s h o r t p e r i o d e l a p s i n g b e t w e e n (
a ) t h e c e s s a t i o n
of the natural respiration (on account of the thoracic wall being cut through), and ( b ) the
moment at which the state of the heart became visible. By this mode of experiment I have
seen distinct evidence of cardiac dilatation caused by the inhalation of chloroform in the usual
way, even though when it had not been carried to such an extent as to paralyse the respiration,
and when there were no abnormal conditions to be considered.
7. The evidence obtained from an inquiry into the mode in which chloroform proves
dangerous gives information of great importance. Undoubtedly, in the great majority of cases
of chloroform collapse, the respiration stops before the heart action has become entirely
ineffective. Indeed,. in healthy animals, at the time the respiration stops and for a variable
period afterwards, the heart, though dilated, is as a rule, quite able to play its part in main-
taining a blood-pressure which, though low, is compatible with the continuance of life.
This is, I believe, by far the most common condition in healthy animals. The heart is directly
acted upon by chloroform, with the result of inducing a more or less extensive dilatation of
its chambers; but this depression does not, in the majority of cases, assume lethal propor--
tions until the respiration has been arrested. The cardiac change is usually not sufficient by
itself to induce a fatal result; when death occurs, the depression of the heart is commonly
associated with vaso motor and respiratory failure. But since the heart is directly acted on
by chloroform, and that to a variable extent, it would not be surprising if, in some cases at
*The conjunctival reflex is, in cats, an excellent guide to the general conditions of the animal, though, as in the
human subject, there are occasionally slight variations in the time at which it becomes abolished.