142 
MESSRS. W. H. HOWELL AND F. DONALDSON 
gave about y^oo as the ratio of the weight of blood thrown out at each systole to 
the body weight. 
Before passing on to a discussion of the results of our work it will be necessary to 
give a brief description of the manner in which observations were made. The appara¬ 
tus and the method of operation were the same as those described by Professor 
Martin (Phil. Trans., 1883, p. 663). Our Dogs, however, were always anaesthetized by 
means of a mixture of chloroform and ether, and great care was taken to introduce 
into the aorta a cannula with as large a bore as possible. 
As quickly as possible after the Dog was in the warm chamber, all the connexions 
made and the heart going well, observations were begun in order to complete a series 
before pulmonary oedema commenced to impede the flow of blood from the right to 
the left side of the heart. The chief point in an observation was to determine the 
quantity of blood pumped out from the left ventricle in thirty seconds. In order to 
accomplish this, one of us took charge of the kymograph, upon the roll of paper of 
which was made to write on the same vertical line the pens of two manometers (one 
recording mean pressure, the other the pulse rate), and of the chronograph, and a 
marking pen to indicate the period during which the blood was collected from the 
outflow tube. This person, when an observation was to be made, after allowing the 
kymograph to run for a few seconds in order to see that the pens were all writing 
properly,, counted aloud 30 seconds, pushing down the handle of the marking pen 
at the beginning of that time and holding it in that position until the 30 seconds 
had been counted. The other person meanwhile collected the blood pumped out from 
the left ventricle daring this time by simply moving the end of the outflow tube S 
(Plate 7) from the funnel x to a graduated cylinder at the beginning of the 30 
seconds, and back again to the funnel at the end. The kymograph was then stopped, 
the observation numbered upon the roll of the kymograph paper and also in the note¬ 
book, and the quantity of blood pumped out, the time of the observation, the venous 
pressure used during the observation, and the temperature of the blood flowing into 
the heart as given by the thermometer p, noted down. After the conclusion of an 
experiment the tracings were carefully examined, and the pulse-rate and the mean 
arterial pressure during each observation ascertained. After each observation, in 
place of the blood collected, about an equal amount of warmed blood, a supply of which 
was kept at hand, was poured back into the receiving flask through the funnel F. 
In giving the results of our experiments, it will be convenient to consider them 
under four different heads, viz.:— 
I. The maximum quantity of blood which can be thrown out from the left ventricle 
at a single systole. 
II. The influence of variations of arterial pressure on the work done by the heart. 
III. The influence of variations of venous pressure on the work done by the heart. 
IV. The influence of variations of pulse-rate on the work done by the heart. 
