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was the case in my experiments, the amount of chloroform vapour in the air never exceeding
four per cent.
(2) On the other hand, there is decisive proof that pulmonary obstruction was not
present i n my experi ment s. Obst ruct i on of t he ci rcul at i on woul d necessari l y cause di st ensi on
of the pulmonary artery as well as, and indeed earlier than, distension of the right heart. The
pulmonary artery would become large and tense in consequence of the increased peripheral
resistance to the outflow of blood from that vessel. Then the increased tension would react
upon the right heart and cause distension there also. But in my experiments there was no
distension of the pulmonary artery during the administration of chloroform. The vessel did not
become distended; it was soft and compressible, and the tension within it was low. It is quite
certain then that pulmonary obstruction could not have been the cause of the dilatation even of
the right side of the heart.
(3) Even if pulmonary obstruction had been present—as was not the case—such
obstruction could not have produced the condition which I described, or anything at all
similar to it.
I have on various occasions purposely brought about a condition of pulmonary obstruc-
tion by mechanical means with a view to studying the features of this condition. This I did
by injecting into one of the great systemic veins some particulate substance, e.g., lycopodium
powder, which would cause embolism of the pulmonary vessels, and so obstruct the circulation
in the lungs. When such a substance is injected into the vein it rapidly passes through the
right heart into the pulmonary vessels, speedily causing more or less extensive and sudden
obstruction of the pulmonary circulation, according to the amount and suddenness of the
injection.
The effects resulting from the plugging of the minute pulmonary vessels induced in this
way are very noteworthy, and illustrate clearly the consequences of obstruction of the circula-
tion in the lungs. The pulmonary artery swells up and becomes largely distended, while at
the same time the vessel feels hard and tense to the touch; the pressure within the vessel is
greatly elevated. The right ventricle and the right auricle then partake in the condition of dis-
tension, being unable to discharge their contents in the normal fashion in face of the greatly
augmented resistance in front. The lungs become pale and anæmic. Meanwhile, it is important
to observe that the left auricle becomes small and collapsed-looking, in consequence of the
obstacle offered to the passage of the blood through the lungs. Strong respiratory efforts, with
convulsions of the asphyxial type (accompanied by spasmodic contraction of the systemic
arteries) supervene in consequence of the stoppage of the respiratory purification of the blood;
the medullary centres become violently stimulated by the venous character of the blood.
Death speedily follows.
It is unnecessary to enter closely into a comparison, or rather contrast, of the typical
illustration of pulmonary obstruction here afforded, and the condition of cardiac dilatation which
I have described as occurring under the influence of chloroform. It is obvious that obstruction
of the circulation in the lungs produces changes strikingly different from those that result from