22D, ON THE CIRCULATION IN 
pounds. The left carotid artery was isolated without loss of blood, a tube secured in the 
opening, and the following record obtained : 
TIME. PRESSURE. REMARKS. 
Minimum. Maximum. 
6.34 37 MM. 47 MM. 
6.6 35 44 
6.63 35 44 
6.10 35 44 
6.11 36 47 Respiratory act. 
6.18 32 38 
6.183 30 37 
6.26 33 41 Tube cleaned. Minute loose clot in artery. 
6.29 36 46 
6.295 4] 53 Respiratory act. 
6.323 os 46 
49 59 After violent movement and repeated respiration. 
32 43 Steady and regular. 
The above observations are given in full, as an example of the mode of conducting the 
experiments. In every case, the extreme pressures were noted; but no complete record 
was kept of the influence of every respiratory act or muscular movement. Very little 
trouble was given by the clotting of the blood in the vessel or tubes, and even when 
clots did form, they were so loose in texture as scarcely to interfere with the registration 
of pressure, 
In the experiments of Poiseuille, Volkmann, and Vierordt, the mean between the ex- 
tremes of the rise and fall was given as the standard of arterial blood-pressure, and the 
instrument used was some form of Poiseuille’s hemadynamometer. M. Bernard has since 
shown that the hemometer of Magendie, which he terms the cardiometer, is a better 
instrument for exhibiting the changes of circulation with rapidity and exactness, and that, 
moreover, its registration gives higher numbers for the pressures than the older instru- 
ment. Having made use of the same apparatus in my own researches, I have preferred 
to follow M. Bernard’s method of notation, which may be easily explained in a few 
sentences. 
This distinguished observer states that when the cardiometer is connected with the 
artery of an animal the mercury rises to a varying height, which he calls the arterial 
pressure, believing it to be due, in part at least, to the elasticity and vital contractility 
of the arterial walls. Each pulse of the heart elevates the column of mercury to a 
certain point above this, whence again it falls during the diastole of the ventricles. The 
excess of mercury thus lifted he takes to represent the power of the heart’s systole. Both 
of the numbers thus obtained may vary with the individual and with the respiratory and 
other movements of the body. M. Bernard holds the view that the arterial tension is 
not due alone to the injecting power of the heart, and that certain agents, which alter the 
heart-force, do not diminish the arterial tension, whilst other substances which plainly 
