248 



PHYSIOLOGY OF THE HEART 



[CH. XXI. 



blood and passes into the circulation. At a convenient point of the vascular 

 system, a sample of blood is drawn off just before the injection, and an equal 

 amount during the passage of the salt ; the quantity of the sodium chloride 

 solution which must be added to the first sample in order that it may contain 

 as much as the second sample is determined. This determination gives the 

 extent to which the salt solution has been mixed with the blood in the heart, 



and knowing the quantity of the solu- 

 tion which has run into the heart, the 

 output in a given time can be calculated. 

 All these experiments have been on 

 animals. The results obtained neces- 

 sarily vary with the size of the animal 

 used, and with the rate at which the 

 heart is beating. If the same relation- 

 ship holds for man as for animals, 

 Stewart calculates that in a man weigh- 

 ing 70 kilos the output of each ventricle 

 per second is less than '002 of the body 

 weight, i.e., about 105 grammes of 

 blood per second, or 87 grammes (about 

 80 c.c.) per heart-beat with a pulse rate 

 of 72. 



An instrument called the cardi- 

 ometer was invented by Roy for regis- 

 tering the output of the heart. His 

 instrument was made of metal, and oil 

 was used as the transmitting medium 

 in its interior. A simple modification 

 of this applicable to the heart of a small 

 mammal like a cat has been devised by 

 Barnard. It consists of an india-rubber 

 tennis ball with a circular orifice cut in 

 one side of it large enough to admit the 

 heart ; a glass tube is securely fixed into 

 a small opening on the opposite side 

 of the ball. The animal is anaesthetised, 

 and its thorax opened. The animal is 

 kept alive by artificial respiration. 

 The pericardium is then opened by a 

 crucial incision, the heart is slipped into 

 the ball ; the pericardium overlaps the 

 outside of the ball, and the apparatus 

 is rendered air-tight by smearing the 

 edges of the hole with vaseline. The 

 four corners of the pericardium are then 

 tightly tied by ligatures round the glass 

 tube just mentioned. This tube is con- 

 nected by a stout india-rubber tube to 

 a Marey's tambour or a piston-recorder, 

 the writing-point of which is applied to 

 a moving blackened cylinder. When 



FIG. 228. Stolnikow's apparatus. A and B are 

 two cylinders fitted with floats provided with 

 writing-points at their upper ends. The tube 

 from the lower end of each bifurcates into 

 two, a and v from A ; a! and v' from B. a and 

 a' are united together and enter the right 

 carotid artery ; v and v' unite and are inserted 

 into the superior vena cava. The remaining 

 branches of the aorta and the inferior vena 

 cava are tied. B is first filled with defibrin- 

 ated blood, which passes down v' into the 

 right auricle, thence to the right ventricle, 

 lungs (where it is oxygenated), and then 

 enters the left side of the heart ; the left 

 ventricle expels it by the tube a into A, so 

 that the float in A rises while that in B falls. 

 As soon as B is empty the tubes v and a' 

 which were previously clamped are released, 

 and v' and a are clamped instead. The left 

 ventricle now expels its blood by the tube a' 

 into the cylinder B ; simultaneously A empties 

 itself through v into the right side of the 

 heart. Zigzag lines are thus traced by the 

 writing-points on the top of the floats, and 

 their frequency enables one to estimate the 

 output of the left ventricle in a given time. 

 (After Starling.) 



the heart contracts, air will be with- 

 drawn from the tambour to the cardi- 

 ometer ; when the heart expands, the air will move in the reverse direction. 

 .These movements are written by the end of the lever of the tambour, and varia- 

 tions in the excursions of this lever correspond with variations in the amount of 

 blood expelled from or drawn into the heart with systole and diastole respec- 

 tively. By calibrating the instrument the actual volume of the blood expelled can 

 be ascertained. 



