672 
PROFESSOR H. N. MARTIN ON THE INFLUENCE OF VARIATIONS 
one another on the paper of a Ludwig’s large kymograph. Below them, in the same 
vertical line, a chronograph pen inscribes seconds. 
As soon as the carotid cannulas are inserted the front of the warm chamber (which 
had been removed to admit of placing the animal inside and performing the above 
described manipulations) is replaced. The gas burners below the trough supporting 
the warm chamber are turned up, and a pause made before beginning observations 
until the air in the chamber, which has been much cooled while the front was away, is 
again heated up to about 38° C. ; and also until at least twenty minutes have elapsed 
since the complete occlusion of all the systemic circulation except that through the 
coronary vessels. Before the lapse of this time all signs of any activity of the extra- 
cardiac nerve centres cease, and the physiologically isolated heart is ready for experiment 
under conditions in which venous pressure, arterial pressure, and the temperature of 
the blood flowing through it are under very complete control. 
By raising or lowering the Mariotte’s flasks, C and D, venous pressure ( i.e ., the 
pressure under which blood enters the right auricle) can be varied within wide limits. 
In the experiments described in the present paper it was always kept at that exerted 
by the weight of a column of defibrinated Calf’s blood 15 centims. in height, except 
when the contrary is expressly stated. Aortic pressure can be varied by sliding the 
support Q, which carries with it the exit of the aortic outflow tube, up or down the 
vertical rod It. Only the lower part of this rod is represented in the figure ; its upper 
end reaches to the ceiling of the room. In most experiments the height of Q was 
arranged so that the mean pressure in the carotid was about 100 millims. of mercury. 
I had supposed before trial that I could in this way keep mean arterial pressure abso¬ 
lutely constant. But in spite of the small resistance offered by the wide aortic cannula 
and the wide system of tubes leading from it to the outflow point S, it turned out that 
the pressure as measured in the carotid (and therefore in the aortic arch) did not 
depend entirely and simply on the difference of level between the root of the aorta and 
the aperture of S. The left ventricle pumped out so much blood as to get up some 
elastic tension in the aortic arch and the arterial stumps still connected with it, and the 
pressure due to this was added to that dependent on the height of the column of blood 
against which the heart worked and on friction in the outflow tubes through which it 
was driven. So long as the heart works with sufficient force to pump blood up to and 
out of S the resistance due to the weight of the column of blood to be lifted remains the 
same ; if the rate of flow be slower, the resistance, and therefore the increased pressure 
due to friction, will be diminished, but in such wide tubes probably only to a trivial 
extent. When, however, any cause, such as change in temperature, deterioration in 
quality of the blood supply, impediment in the pulmonary flow, or gradual death of 
the isolated heart, influences the amount of blood pumped out in the unit of time by 
which have been cast upon the accuracy of this instrument when a very slow or a very quick pulse is to 
be recorded, the Fick manometer was subsequently added. It turned out, however, that this was unne¬ 
cessary ; the pulse-rate recorded by both manometers was exactly the same. 
