MOVEMENTS OF RESPIRATION ON THE CIRCULATION OF THE BLOOD. 57 T 
completed by a vulcanite tube filled with solution of carbonate of soda* * * § . It having 
been ascertained that the apparatus was in order, and the dog breathing quietly, the 
clockwork was set in motion, the rate of horizontal movement of the paper being 1 inch 
in six seconds. The tracings show that there were about nine respirations and 108 pul- 
sations per minute. The upper or arterial tracing is crossed by a faint horizontal line, 
which indicates a pressure of 6'2 inches of mercuryf. During the progress of the 
observations the brushes were simultaneously withdrawn from the paper at short inter- 
vals, so that synchronical points could be accurately taken. The tracings show that the 
period occupied by each respiratory act is divisible into two parts, one of which (about 
two-fifths of the whole) is occupied by the thoracic movements, the remainder by the 
pause. Of the first part, two-thirds correspond to inspiration, one-third to expiration. 
It is further seen that the effects of the thoracic movements are as readily discernible in 
the respiratory as in the arterial tracing. The part of each arterial tracing correspond- 
ing to a single respiratory interval consists, as described by Ludwig, of a great wave, the 
contour of which is broken by smaller waves, each representing a contraction of the 
heart. During the whole period of the pause the arterial pressure gradually sinks. 
The commencement of inspiration is immediately followed by an increase of pressure, 
which becomes still more marked during expiration ; but no sooner is the expiratory act 
completed than it again subsides. The apex of the greater or respiratory wave in the 
arterial tracing is therefore coincident with the end of expiration. As regards the effect 
of the thoracic movements on the duration of each cardiac revolution, it is no less di- 
stinctly seen that the interval between each two succeeding contractions is about three 
times as great in those pulsations which immediately follow the end of expiration as in 
those which precede it, and that this interval gradually diminishes until the next corre- 
sponding period. At one part of the tracing, where the inspiration lasted longer and 
was deeper than usual, it is seen that the consequent elevation of pressure and accelera- 
tion of pulse was greater J. 
Observation II.— June 16th, 1865 (Plate XXIII. fig. 2). 
The animal employed was a male mongrel dog of moderate size. The experimental 
method was the same as before, with the exception that the rate of movement of the 
paper was about twice as quick. The synchronical points are marked by simultaneous 
interruptions, and by dots indicating the relative position of the brushes §. The faint 
* In my earlier experiments, although a saturated solution was always used, the blood sometimes coagulated 
before the observation was completed, rendering it necessary to remove, cleanse, reinsert, and reconnect the 
silver canula. To prevent this result a pressure of about 5 inches of mercury, i. e. nearly equal to that usually 
existing in the arteries of a dog, was first produced in the dynamometer (by a mechanical arrangement which it 
is not necessary to describe) before completing the connexion. When this precaution was taken, very little 
blood passed beyond the silver tube in the artery, and even there was mixed with the saline solution in such 
proportion that no coagulation took place. 
t The absolute value of this result is subject to the exception made at p. 575. 
X This animal was afterwards employed in an experiment on asphyxia. 
§ These faint horizontal lines and the dots have been omitted in the engravings. 
