MECHANICS OF THE CIRCULATION IN THE VESSELS 139 



of i '92 metres that is, about 8*64 kilogramme -met res'; in 24 hours it 

 would be, say, 12,450 kilogramme-metres. Taking the mean pressure 

 in the pulmonary artery at one-third of the aortic pressure, we get for 

 the daily work of the right ventricle about 4,150 kilogramme-metres. 

 The work of the two ventricles is thus about 16,600 kilogramme-metres,* 

 which is enough to raise a weight of nearly 4 pounds from the bottom 

 of the deepest mine in the world to the top of its highest mountain, or 

 to raise the man himself to i times the height of the spire of Strasburg 

 Cathedral, or twice the height of the loftiest ' skyscraper ' in New York. 

 By friction in the bloodvessels this work is almost all changed into its 

 equivalent of heat, nearly 40,000 gramme-calories (p. 663) . Further, since 

 the contraction of the heart is always maximal (p. 154), and there is 

 reason to believe that the quantity of blood ejected at a single systole 

 by the left ventricle (being dependent upon the inflow from the pulmon- 

 ary veins, and therefore upon the inflow into the right side of the heart 

 from the systemic veins) varies widely, some of the mechanical effect 

 of the contraction must be wasted when the quantity is less than the 

 ventricle is capable of expelling. 



Output of the Heart. If -4^ kilos of blood pass through the heart in 

 i minute with the average pulse-rate of 72 per minute, the quantity 



ejected by either ventricle with every systole will be - - = 62-5 grm., 



or a little less than 60 c.c. The output may be expressed in grammes 

 or cubic centimetres per minute (the minute volume), or per second, or 

 per beat. It has been measured in animals in several ways e.g., by 

 inserting a stromuhr (p. 121) on the course of the aorta, or by recording 

 the variations in the volume of the heart, or, better, of the ventricles, 

 by means of a plethysmograph (cardiometer of Henderson), in which 

 the organ is enclosed. Another method, which does not entail the 

 opening of the chest, is to allow a salt solution to run slowly, for a de- 

 finite number of seconds, into the left ventricle through a tube passed 

 into it from the carotid artery. A sample of the mixture of blood and 

 salt solution is collected from a branch of the femoral artery, where its 

 arrival is detected by the change of electrical resistance (p. 135). From 

 the amount of salt solution which must be added to a normal sample 

 of blood drawn before the injection to make its conductivity the same 

 as that of the sample taken during the passage of the mixture, the 

 quantity of blood with which the solution was mixed in the ventricle 

 during the injection can be approximately determined. By this method 

 it has been shown in a series of experiments on more than twenty dogs, 

 ranging in weight from 5 to nearly 35 kilos, that the output of the 

 left ventricle per kilo of body-weight per second diminishes as the size 

 of the animal increases ; and the relation between body-weight and out- 

 put is such that in a man weighing 70 kilos we can hardly suppose that 

 the ventricle discharges, during bodily rest, more than 105 grm. of 

 blood per second, or 87 grm. (80 c.c.) per heart-beat with a pulse-rate 

 of 72. Putting this result along with that deduced from the circulation- 

 time, we can pretty safely conclude that the average amount of blood 

 thrown out by each ventricle at each beat is not more than 70 or 80 c.c. 

 Zuntz, from the quantity of oxygen absorbed by the blood in the lungs 

 in a definite short time, and the difference between the oxygen content 

 of samples of the arterial and venous blood, has estimated the output 

 per beat at 60 c.c. But according to him this may be doubled during 



* Since the blood on expulsion is moving with a certain velocity, an addi- 

 tion might be made for its kinetic energy. But this would only increase the 

 total work by a small fraction (about i per cent.). 



