240 ENDOCARDIAC PRESSURE. [BOOK i. 



in the cavities of the heart, i.e. shews that the pressure in them may 

 fall below that of the atmosphere. Thus in the left ventricle (of 

 the dog) a minimum pressure varying from 52 to 20 mm. may 

 be reached, the minimum of the right ventricle being from 17 to 

 16 mm., and of the right auricle from 12 to 7 mm. 1 Part of 

 this diminution of pressure in the cardiac cavities may be due, as 

 will be explained in a later part of this work, to the aspiration of 

 the thorax in the respiratory movements. But even when the 

 thorax is opened, and artificial respiration kept up, under which 

 circumstances no such aspiration takes place, a negative pressure is 

 still observed, the pressure in the left ventricle still sinking as low 

 as 24 mm. Now, what the instrument actually shews is that at 

 some time or other during the number of beats which took place 

 while the instrument was applied (and these may have been very 

 few) the pressure in the ventricle sank so many mm. below that of 

 the atmosphere. Since the negative pressure is observed when the 

 heart is beating quite regularly, each beat being exactly like the 

 others, we may infer that a negative pressure occurs at some period 

 or other of each cardiac cycle. But the instrument obviously gives 

 us no information as to the exact phase of the beat in which the 

 negative pressure occurs ; to this point as well as to the import- 

 ance of this negative pressure we shall return presently. 



132. The difficulties due to the inertia of the mercury may 

 be obviated by adopting the method of Chauveau and Marey which 

 consists in introducing, in a large animal such as a horse, through 

 a blood vessel into a cavity of the heart, a tube ending in an 

 elastic bag, Fig. 37 A, fashioned something like a sound, both tube 

 and bag being filled with air, and the tube being connected with 

 a recording ' tambour.' 



A tube of appropriate curvature, A. b. Fig. 37, is furnished at its 

 end with an elastic bag or * ampulla ' a. When it is desired to explore 

 simultaneously both auricle and ventricle, the sound is furnished with 

 two ampullae with two small elastic bags, one at the extreme end and 

 the other at such a distance that when the former is within the cavity 

 of the ventricle the latter is in the cavity of the auricle. Such an 

 instrument is spoken of as a ' cardiac sound.' Each ' ampulla ' com- 

 municates by a separate air-tight tube with an air-tight tambour 

 (Fig. 37 B) on which a lever rests, so that any pressure on the ampulla 

 is communicated to the cavity of its respective tambour, the lever of 

 which is raised in proportion. When two ampullae are used the 

 writing points of both levers are brought to bear on the same re- 

 cording surface exactly underneath each other. The tube is carefully 

 introduced through the right jugular vein into the right side of the 

 heart until the lower (ventricular) ampulla is fairly in the cavity of 

 the right ventricle, and consequently the upper (auricular) ampulla 

 in the cavity of the right auricle. Changes of pressure on either 



1 These numbers are to be considered merely as instances which have been 

 observed, and not as averages drawn from a large number of cases. 



