134 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



cuspid valve, and now, upon the opening of this, it botli flows and is to some 

 slight degree drawn into the ventricle. This blood is followed by that which, 

 during the remainder of the "repose of the whole heart," moves through the veins 

 and the auricle into the ventricle under the influence of the arterial recoil and 

 the other forces which cause the venous flow (p. 93) ; and the charge of the 

 ventricle is completed by the blood which is injected at the auricular systole. 



The Negative Pressure within the Ventricles. — That the heart, in its 

 diastole, draws something from without into itself is a very ancient belief, and 

 this mode of its working played a great part in the doctrines of Galen and of 

 the Middle Ages. In 1543, Vesalius, who, on anatomical grounds, questioned 

 some of Galen's views as to the cardiac physiology, fully accepted this one. 1 

 On the other hand, in 1628, Harvey rejected it. "It is manifest," he says, 

 " that the blood enter- the ventricles not by any attraction or dilatation of the 

 heart, but by being thrown into them by the pulses of the auricles." : In this 

 particular, modern research in some degree confirms the opinion of the ancients, 

 while denying to suction within the ventricles any such great effect as was 

 once believed in. As a rule, the cuspid valve is not opened till the pressure in 

 the ventricle has fallen to a point not far from the pressure of the atmosphere ; 

 it may be even below it. In any case the ventricular pressure usually becomes 

 negative very soon after the opening of the cuspid valve. This negative pres- 

 sure is of variable extent and continues for a variable time. It is always 

 small as compared with the positive pressure of the systole. Under 

 some circumstances negative pressure may be absent, but it is so very com- 

 monly present as certainly to be a normal phenomenon (sec Figs. 22, 

 2o, and 24). This negative pressure is revealed by the elastic as well 

 as by the minimum mercurial manometer; it is present in both ventri- 

 cles ; and it is present, to a less degree, even after the chest has been 

 opened, and its aspiration destroyed. It is in virtue of the forces which 

 produce the negative pressure in the manometer that blood is drawn into 

 the heart. 



Passing by disproven or improbable theories as to the causes of this suction, 

 we -hall find the following statements justified: As the heart lies between the 

 lungs and the chest-wall (including in this term the diaphragm), it is subject, 

 like the chest-wall and the great vessels, to the continuous aspiration produced 

 by the stretched fibres of the elastic lungs. At every inspiration this aspiration 

 is increased by the contraction of the inspiratory muscles. We see, therefore, 

 that the ventricle must overcome this aspiration as part of the resistance to its 

 contraction; and that, as soon as that contraction has ceased, the walls of the 

 ventricle must tend to be drawn asunder by those same forces of elastic recoil 

 in the pulmonary fibre-, and of contraction of the muscles of inspiration, which 

 we have -ecu (p. 95) to produce a slight -net ion within the great veins in and 



1 Andrea Vescdii BruxeUensis, Schola medicorvm Patavince professoris, <!>■ Humani corporis 

 fabrica Libri septan. Basilese, ex officina [oannis Oporini, Anno Salutie reparatse MDXLIIL 

 Page 587. 



2 Op. cit., 1628, p. 26: Willis's translation, Bowie's edition, 1889, p. 28. 



