228 ON THE CIRCULATION IN 
surfaces. A very simple experiment finally decided the nature of the motion above 
described. 
ExprerRIMENT.—A tube having been placed in the right carotid artery was connected with 
the hemometer. A second tube, fitted to the cut trachea, was so bent as to be allowed 
to dip just below the surface of a vase of water. On bringing the arterial and tracheal 
tubes near together, the rise and fall of the fluids in both was found to be exactly syn- 
chronous. The pulsatile motion perceived in the flanks and transmitted through the 
lungs, as shown above, seems, therefore, to be due to the propagated impulses from the 
neighboring vessels, and, perhaps, in part also from the pulmonary arteries. 
During the interval between two respirations the column in the hemometer tube rose 
and fell with singular steadiness at times. The long expiration which begins the series 
of respiratory motions, had no marked effect on the column sustained. The long inspi- 
ration which followed caused a small rise in the mercury, and the short incomplete expi- 
ration which terminated the series of movements raised it still higher. 
The following experiment will serve to exemplify the amount and character of this 
influence. 
Snapper. Weight 194 lbs. Temp. 70° F. Pulse 33. Tube in the left carotid: 
TIME. MINIMUM. MAXIMUM. DIFFERENCE. RESPIRATORY STATE. 
4.10 P.M. 34 MLM. 45 M.M. 11 M.M. 
4.12 34 44 10 Expiration. 
36 46 10 Inspiration. 
40 51 11 Short expiration. 
4.143 33 40 7 Expiration. 
33 41 8 Inspiration. 
39 49 10 Short expiration. 
In mammals it is easy to see why active expiration should cause an increased pressure 
in the arteries, since the thorax is contracted and the belly drawn in so as to exert con- 
siderable compression upon the large arteries, and thus to cause an instant rise in the 
manometric column of mercury attached to an artery. In the Turtle the first respiratory 
act is a slow one, and the amount of force employed in effecting it but small; whence no 
marked influence is visible in the arteries. The long inspiration which follows usually 
increases a little the arterial pressure, although sometimes, where the action of breathing 
is not energetic, no such effect can be seen. ‘The cause of the slightly increased pressure 
alluded to above I have been unable to fathom. ‘The short expiration which completes 
the respiratory series at once raises the arterial pressure. ‘This is, probably, due to the 
fact that at this time the lung distended with air is favorably situated to exert direct 
pressure on neighboring vessels, and also to the fact that this final expiratory motion is 
vigorous and abrupt. 
