CHAPTEK VIII 



THE BLOOD-STKEAM : MOVEMENT IN THE VESSELS 



SUMMARY. 1. .Fundamental laws of hydrodynamics for passage of fluid through 

 rigid tubes. 2. Application of these laws to haemodynaiuics. 3. Mechanical 

 effects of elasticity of vessel walls and intermittence of flow of blood from heart ; 

 laws of wave motion. 4. Method of measuring and automatically registering 

 variations in blood pressure. 5. Principal results obtained. 6. Methods of measur- 

 ing velocity of circulation ; experimental results. 7. Sphygmography and sphygmo- 

 grams representing pulsatory oscillations in pressure. 8. Comparison of cardiograms 

 and sphygmograms registered simultaneously, indicating duration of principal 

 phases of cardiac cycle in man. 9, Comparison of several sphygmograms registered 

 simultaneously from arteries at different distances from the heart, indicating rate 

 of transmission of primary and of dicrotic wave. 10. Tachymetry and tachygrams 

 representing pulsatory variations in current velocity. II. Plethysmography and 

 plethysmograms representing pulsatory oscillations in the volume of the arteries. 

 12. Schema of mechanical conditions of the circulation in the three great vascular 

 systems ; determination of duration of the entire circulation. Bibliography. 



WHEN the circulation is observed under the microscope (see Chap. 

 VI., 8) it is easy to detect a phenomenon which is among the 

 most fundamental in Haemodynamics : the movement of blood in 

 the vessels is continuous ; continuous and rhythmically accelerated 

 in the arteries, continuous and constant in the veins. The analysis 

 of this complex phenomenon in its details and in its elements, the 

 determination of the mechanical conditions on which it depends, 

 and the laws by which it is governed, form the contents of this 

 chapter. 



I. The movement of the blood from the heart through the 

 vessels is regulated and determined, like the movement of water 

 driven rhythmically through a tube from a pump, by two 

 antagonistic influences : the energy developed from the heart, or 

 pump, which drives the fluid through the vessels; and the 

 resistance represented by the internal walls of the vessels, owing 

 to the adhesion of the fluid, and its viscosity. The velocity of each 

 molecule of fluid is proportional to the difference between the 

 impulses felt by each a tergo and a f route. The more the driving 

 force overcomes the sum of the resistances, the faster will be the 

 flow of a fluid through the system. In order, however, to 

 form a more exact and concrete idea of the mechanism of the 

 movement of fluids, it will be well to review certain principles 



232 





