226 PHYSIOLOGY CHAP. 



which cover it to a great extent : but during the period of passive 

 diastole or repose, its walls are soft and easily compressible, while 

 in the systolic period they become, hard and tense, and this is 

 enough to determine the phenomenon of ictus. This theory, 

 adumbrated by Harvey, was clearly set forth by Kiwisch (1846), 

 and upheld more recently by Bamberger, and by Chauveau and 

 Faivre (1856) ; but Marey (1863-76) was the first to give convincing 

 proof of its accuracy by his ingenious schemata of the movements 

 of the heart. He succeeded with these in producing artificial 

 cardiograms, which exhibit all the most important features of the 

 cardiograms obtained on man, as shown in the two tracings of 



Fig. 81. 



The analytical study of these features is of great scientific and 

 practical interest, but we must consider them together with the 

 waves exhibited by the arterial pulse and the sphygmograuis, with 

 which they are intimately connected by their origin. 



X. The systolic movements of the heart in the period of tension 

 must, since they determine a sudden elevation of the intercostal 

 spaces of the precordial region, produce a rhythmical dilatation of 

 the thoracic cavity, in proportion with the energy and rapidity of 

 the impact. Further, the diminution of the total volume of the 

 heart during the period of systolic efflux until it reaches meiocardia 

 is commensurate with the quantity of blood expelled from the 

 arteries. Half this blood, passing through the pulmonary system, 

 does not leave the thoracic cavity ; but the other half, passing 

 through the aortic system, issues rapidly from the thorax, pro- 

 ducing a comparative vacuum, which cannot be compensated by 

 the blood that simultaneously enters the thorax by the venae 

 cavae. During systole, therefore, the thoracic cavity must, in 

 virtue of distinct mechanical conditions which succeed each other, 

 develop an aspiration, capable of being felt in the intercostal 

 spaces not in contact with the heart in the lungs, the diaphragm 

 and the veins adjacent to the thorax. 



In thin persons it is, in fact, easy to see coincidently with 



systole, a depression of the intercostal spaces, to which the name of 



negative cardiac pulse has been given (to distinguish it from the 



positive pulse that can be observed in the region of the apex of 



the heart and its vicinity). At the same moment there is also a 



v negative pulmonary pulse, i.e. a gentle inspiratory movement of 



the lungs which, when the glottis is open, may produce a systolic 



diminution in the pressure of the air contained in the buccal cavity 



> or nasal fossae. It is also possible to detect a negative pulse of 



v the abdominal wall in the epigastric region, which is the effect of 



an aspiration exerted by the thoracic cavity on the diaphragm. 



Lastly, it is possible also to observe a negative systolic pulse in the 



, jugular veins due to the same cause, although here it is probable 



that other mechanical factors co-operate, which are independent of 



