THE HEART BEAT. 493 



a suction-pump, sucking in blood from the venous side in conse- 

 quence of an active dilatation. According to this view, the heart 

 works after the manner of a syringe bulb, which when squeezed 

 forces out liquid from one end and when relaxed sucks it in from 

 the other in consequence of its elastic dilatation. While this view 

 has long been entertained, modern interest in it was aroused chiefly 

 perhaps by the experiments of Goltz and Gaule, which showed that 

 at some point in the heart beat there is or may be a strong negative 

 pressure in the interior of the ventricles.* Their method consisted 

 in connecting a manometer with the interior of the ventricle and 

 interposing between the two a valve that opened only toward the 

 heart. The manometer was thus converted into a minimum 

 manometer, which registered the lowest pressure reached during 

 the period of observation. By this method they and others have 

 shown that in an animal (dog) with an opened thorax the pressure 

 in the interior of the ventricles may be negative to an extent equal 

 to 20, 30, or even 50 mms. of mercury. Moreover, by the use of 

 some form of elastic manometer, such as the Hiirthle instrument 

 (p. 449), it has been shown that this negative pressure occurs at the 

 end of the period of relaxation, at the time, therefore, at which it 

 might be supposed to exert a marked influence upon the inflow of 

 venous blood. It should be added, however, that a negative 

 pressure can not be shown for every heart beat. It may be absent 

 altogether or slight in amount, varying, no doubt, with the force of 

 contraction and the condition of the heart. Physiologists have 

 attempted to determine the cause of this negative pressure and the 

 extent of its influence on the blood-flow. With regard to the first 

 question, so many answers have been proposed that it is difficult 

 to arrive at a satisfactory opinion. According to some, the heart 

 tends to dilate at the end of its systole by virtue of its own elasticity, 

 that is, the elasticity of its own musculature or of the connective 

 tissue contained in its substance; for example, beneath the en- 

 docardium, in the walls of the arteries, etc. This view, however, 

 finds little or no support from direct experiments made upon the 

 fresh, living heart. If such a heart in a bloodless condition is 

 squeezed by hand there is no evidence of an elastic recoil as in the 

 case of a syringe bulb. Others have explained the negative pressure 

 as due not to a simple elastic expansion, but to what may be 

 called a physiological expansion, that is, an expansion due to 

 physiological processes, such as anabolic changes. Such a view, 

 however, is at present more or less speculative and can not be con- 

 clusively demonstrated. Still others have traced the expansion of 



* For a complete discussion of this subject and the literature see the ar- 

 ticle by Ebstein, " Die Diastole des Herzens," in the " Ergebnisse der Physi- 

 ologic," vol. iii, part n, 1904. 



