FLOW OF FLUIDS THROUGH TUBES. 89 



(2) J. Mttller's Experiment (1838). Conversely, if after the deepest possible 

 expiration the glottis be closed, and the chest be now dilated with a great 

 inspiratory effort, the heart is powerfully dilated, the elastic traction of the lungs, 

 and the very attenuated air in these organs, act so as to dilate the cavities of the 

 heart. More blood flows into the right Heart, and, in proportion as the right 

 auricle and ventricle can overcome the traction outwards, the blood-vessels of the 

 lungs become filled with blood, and thus partly occupy the lung space. Much less 

 blood is driven out of the left heart, so that the pulse may disappear. Hence, the 

 heart is distended with blood and the lungs are congested, while the aortic system 

 contains a small amount of blood, i.e., the systemic circulation is comparatively 

 empty, while the heart and the pulmonary vessels are engorged with blood. 



In normal respiration, the air in the lungs during inspiration is under slight 

 pressure, while during expiration the pressure is higher, so that these conditions 

 favour the circulation ; inspiration favours the occurrence of diastole, the supply of 

 blood (and lymph) through the venae cavse. In operations where the axillary or 

 jugular vein is cut, air may be sucked into the circulation during inspiration, and 

 cause death. Expiration favours the flow of blood in the aorta and its branches, 

 and aids the systolic emptying of the heart. 



The elastic traction of the lungs aids the lesser-circulation through the lungs; 

 the blood of the pulmonary capillaries is exposed to the pressure of the air in the 

 lungs, while the blood in the pulmonary veins is exposed to a less pressure, as the 

 elastic traction of the lungs, by dilating the left auricle, favours the outflow from 

 the capillaries into the left auricle. The elastic traction of the lungs acts slightly 

 as a disturbing agent on the right ventricle, and, therefore, on the movement of 

 blood through the pulmonary artery, owing to the overpowering force of the blood- 

 stream through the pulmonary artery, as against the elastic traction of the lungs 

 (Donders). 



The above apparatus (fig. 65) shows the effect of the inspiratory and expiratory movements 

 on the dilatation of the heart, and on the blood-stream in the large blood-vessels. The large 

 glass vessel represents the thorax ; the elastic membrane, D, the diaphragm ; P, p, the lungs ; 

 L, the trachea supplied with a stop-cock to represent the glottis ; H, the heart ; E, the venae 

 cavse ; A, the aorta. If the glottis be closed, and the expiratory phase imitated by pushing up 

 D as in I., the air in P, P and the heart H are compressed, the venous valve closes, the arterial 

 is opened, and the fluid is driven out through A. The manometer, M, indicates the intra- 

 thoracic pressure. If the glottis be closed, and the inspiratory phase imitated, as in II., p, p 

 and h are dilated, the venous valve opens, the arterial valve closes ; hence, venous blood flows 

 from e into the heart. Thus, inspiration always favours the venous stream, and hinders the 

 arterial ; while expiration hinders the venous, and favours the arterial stream. If the glottis 

 L and I be open, the air in P, P, p, p will be changed during the respiratory movements D and 

 d, so that the action on the heart and blood-vessels will be diminished, but it will still persist, 

 although to a much less extent. 



The Circulation of the Blood. 



61. FLOW OF FLUIDS THROUGH TUBES. Toricelli's Theorem states that the velocity of 

 -efflux (v) of a fluid through an opening at the bottom of a cylindrical vessel is exactly the 

 same as the velocity which a body falling freely would acquire, were it to fall from the surface 

 of the fluid to the base of the orifice of the outflow. If h be the height of the propelling force, 

 the velocity of efflux is given by the formula 



v=\J2gh (where g = 9 '8 metres). 

 The rapidity of outflow increases with increase in the height of the propelling force, h. The 

 former occurs in the ratio 1, 2, 3, when h increases in the ratio 1, 4, 9, i.e., the velocity of 

 efflux is as the square root of the height of the propelling force. Hence, it follows that the velocity 

 of efflux depends upon the height of the liquid above the orifice of outflow, and riot upon the 

 nature of the fluid. 



Resistance. Toricelli's theorem, however, is only valid when all resistance to the outflow is 



