MOVEMENTS 01 RESPIRATION ON THE CIRCULATION OE THE BLOOD. 591 
sure was repeatedly reduced below the original level, rising again as soon as the former 
method of breathing was resumed. 
Observation XVIII. — August 1st (Tracings not engraved). 
On this occasion a rough mongrel terrier was used. Bate of movement 1 inch in 7T 
seconds. Before section the animal was breathing somewhat irregularly, twenty-seven 
times in a minute, the rate of pulsation being forty-four, and the height of the mercurial 
column being 5 inches ; twenty-three seconds elapsed between the section of the two 
nerves. During this interval the respiratory movements gradually increased in extent 
and became irregular ; but immediately after the second nerve was divided the thoracic 
movements became so violent as to shake the table and apparatus, while the arterial 
pressure rose to 8 inches, remaining at that height for several minutes. The animal 
continued to breathe violently for about sixty seconds, during which period about twenty 
inhalations took place. After this the respiration assumed a more regular character, its 
rate varying from five to six per minute. After the first section the pulse gradually 
increased in frequency, finally attaining a rate of 120 per minute. This rate was main- 
tained for two minutes and a half, when it suddenly diminished to fifty. 
In all the animals I have observed after section of the pneumogastrics I have found 
(1) that the arterial pressure tends to increase during the slow inspiration, and to decline 
during the pause ; (2) that a more rapid increase of tension occurs simultaneously with 
expiration ; and (3) that this last effect, as I have ascertained by repeated measurements, 
never lasts for more than a second. In order to arrive at a satisfactory explanation of 
these facts, it is necessary to consider what is the condition of the heart and circulation 
after section of the vagi. The arterial tracings obtained indicate extreme abbreviation 
of the diastolic period combined with high arterial tension. The contractions of the 
heart follow each other so rapidly that the organ is in a state of continuous thrill, while 
at the same time they are sufficiently vigorous to maintain an arterial pressure several 
inches higher than the normal. In other words, the heart, although it relaxes between 
each contraction and its successor, never has time to empty itself, so that the wdrole 
systemic circulation is unduly distended. All this is sufficiently explained if we assume 
that after section of the pneumogastrics the action of the heart is intensified, the effect 
being altogether analogous to that which results from the injection of air into the lungs 
of a partially asphyxiated animal (see Observations XIII.-XVI.). It is to be further 
noticed that the thoracic cavity is also in a state of permanent distension, in consequence 
of the excessive action of the inspiratory muscles — that is to say the thoracic walls during 
more than half of the respiratory act remain expanded to such a degree that their elas- 
ticity is more than counterbalanced by that of the lungs. 
This being understood, it appears that there are two distinct reasons why the effect of 
inspiration is less marked after section of the vagi than in the normal animal. It is so, 
first, because the diastolic period is already so abbreviated that there is no room for 
further abbreviation ; and secondly, because the veins of the chest being already expanded 
