THE MECHANISM OF THE CIRCULATION. 



But both these conditions are brought about by a method entirely 

 different from that supposed by Briicke. The sinuses of Yalsalva have 

 been evolved for the attainment of two objects. The first of these is 

 the prevention of the seuiilunar valves swinging back so as to adhere 

 to the wall of the artery ; the second is the provocation of eddies which 

 close the valves at the instant systole ceases. Ceradini l has experi- 

 mentally determined that, when fluid is suddenly driven from the 

 ventricle into the pulmonary orifice, the valves do not swing back 

 against the wall of the sinuses. 



THE CHANGES OF PRESSURE ix THE HEART DURING THE 

 CARDIAC CYCLE. 



Method. Dissatisfied with the differences of opinion arising from 

 the mere personal observation of the sequence of events in the cardiac 

 cycle, Chauveau and Marey 2 explored the intracardiac pressure. For 



this purpose they invented a special in- 

 strument, the cardiac sound or sphyg- 

 moscope, by which the variations of 

 pressure in one or other chamber of 

 the heart could be recorded. 



The sound consisted of a hollow 

 metal tube, of such a bore that it 

 could be easily passed down the jugu- 

 lar vein or carotid artery of the horse. 

 At one end of the tube was a wire 

 framework, over which was drawn a 

 thin rubber bag. This end was passed 

 into a cavity of the heart, and the 

 other end was put in connection with 

 a recording tambour. The rubber bag 

 transmitted the changes of pressure 

 in the heart to the recording tambour, 

 and was at the same time, bv means 



" *-<3S!n5 M'~ of the frame rk . Prevented from com- 



pletely collapsing. 



In some experiments, Chauveau and Marey employed a byway 

 sound, consisting of a double tube and two bags. When this' was 

 passed down the jugular vein, one bag was so situated as to lie in the 

 right auricle, and the other in the right ventricle. Each tube of the 

 byway sound passed to a recording tambour, and the levers connected 

 with each tambour wrote exactly beneath one another, and thus the 

 auricular and ventricular pressures were simultaneously recorded on a 

 revolving drum. These records can be taken while the horse quietly 

 eats at its manger, oblivious of the instrument within its heart. 



These and similar instruments are experimentally calibrated against 

 the readings of a mercury manometer. 3 



Many investigators have followed in the steps of Chauveau and 

 Marey. Magini and Eolleston passed hollow trocars directly through 

 the thorax into the cavities of the heart, while Fick, Hiirthle, Fredericq, 

 v. Frey, Krehl, and others, have passed cannulas down the jugular 



1 Loc. tit., S. 60. - Mem. Acad. de m^d., Paris, 1863, tome xxvi. p. 272. 



9 Marey, "Circulation du sang," Fig. 45, p. 111. 



