426 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



On the other hand, in 1628, Harvey rejected it. " It is manifest, 7 ' he says, 

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

 heart, but by being thrown into them by the pulses of the auricles." l 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 (see Figs. 107, 

 108, and 109). 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 shall 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 fibres, and of contraction of the muscles of inspiration, which 

 we have seen (p. 387) to produce a slight suction within the great veins in and 

 very near the chest. These same forces produce a slight suction within the 

 ventricles, relaxed in their diastole. But a very slight suction occurs at each 

 ventricular diastole even after the chest has been opened. The causes of this 

 are still obscure ; but it is to be borne in mind that the relaxing wall of the 

 ventricle, flabby as it is, possesses some little elasticity, especially at the auriculo- 

 ventricular ring, and therefore may tend to resume a somewhat different form 

 from that due to its contraction. As the result of this slight elastic recoil, a 

 feeble suction may occur. 



N. THE FUNCTIONS OF THE AURICLES. 



Connections of the Auricle. Into the right and left auricles open the 

 systemic and pulmonary veins respectively, and each auricle may justly be re- 

 garded as the enlarged termination of that venous system with which it is con- 

 nected. Until modern times the terms of anatomy reflected this view, and 



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



