MOVEMENT OF THE BLOOD IN THE CIRCULATION. 125 



the lungs is prevented from interfering to any marked degree with the 

 action of the right ventricle and, therefore, with the movement of 

 blood through the pulmonary artery, because of the sufficient resistance 

 of the blood, right ventricle and the pulmonary artery against the elastic 

 pulmonary traction. 



The apparatus illustrated in Fig. 36 shows clearly the influence of inspiratory 

 and expiratory movements on the expansion of the heart and on the current of 

 blood in the large vascular channels leading to and from the heart. The large 

 glass bottle represents the thorax, and its bottom has been replaced at D by an 

 elastic rubber membrane, which represents the diaphragm. ' P P are the lungs; L 

 the trachea, the entrance to which (glottis) may be closed by means of a stop- 

 cock; H is the heart; E represents the course of the venae cavae; and A the aorta. 

 When the tracheal stop-cock is closed and the expiratory position, as shown at I, 

 is established by elevating the membrane D, with diminution in the size of the 

 thoracic cavity, the air in P P is condensed, while at the same time the heart H 

 is compressed; the venous valve closes, while the arterial valve is opened and the 

 fluid is driven out through A. The manometer M, inserted into the flask, shows 

 the increased intrathoracic pressure. Again, when the stop-cock 1 is closed (in 

 II), and the membrane is strongly depressed, the lungs pp expand, and with 

 them the heart h. The venous valve opens, while the arterial valve closes, and 

 the venous blood enters the heart through e. Thus, inspiration always hastens 

 the venous and inhibits the arterial flow, while expiration inhibits the venous 

 and hastens the arterial flow. If the glottis (L and 1) remains open, the air in P P 

 and p p naturally is changed as the thorax passes from the inspiratory to the 

 expiratory position (D and d). Accordingly, the effect on the heart (H and h) 

 and on the blood-vessels is smaller, but even under such conditions it must persist 

 in small measure. 



THE MOVEMENT OF THE BLOOD IN THE 

 CIRCULATION. 



TORICELLPS THEOREM ON THE VELOCITY OF ESCAPE OF 



FLUIDS. 



According to Toricelli's law, the velocity (v) with which a fluid escapes, for 

 example, through an opening in the floor of a hollow cylindrical vessel, is equal 

 to the velocity that a freely falling body would attain in 

 falling from the level of the fluid to the level of the open- 

 ing (the height of the propelling force h) . 



Hence v = 1/2 g h; in which g = 9.8 meters. 



The velocity of outflow increases, as has been shown 

 experimentally, as the height of the propelling force 

 (h) increases, and it preserves the ratio of i, 2, 3 

 as the propelling force increases in the ratio of i, 4, 9; 

 that is, the velocity of outflow is proportionate to the 

 square root of the height of the propelling force. It thus 

 follow r s that the velocity of outflow depends solely on the 

 distance between the level of the fluid and the opening, 

 and not on the nature of the escaping fluid. Whenever a 

 fluid is found escaping with a definite velocity, the force 

 that causes the flow may be expressed by the height of 

 a column of fluid (h) in a vessel the height of the pro- 

 pelling force. 



Toricelli's law, however, is applicable only when all FIG. 

 possible resistance that may be offered to the escape of 

 the fluid is left out of account. As a matter of fact, 

 certain resisting forces are present in any physical ex- 

 periment of this kind. Hence, the force that is ex- 

 pressed by the height of the propelling force (h) not 



only causes the escape of the fluid, but also overcomes the sum of all the resist- 

 ances. These two forces may be expressed by the heights of two columns of 

 water superposed the one upon the other ; namely, by the height of the velocity 



37. Pressure- v e s s e 1 

 Filled with Water: h, 

 height of the column of 

 fluid; F, height of the 

 velocity; D, height of the 

 resistance. 



