BY DR. BURDOX-SANDERSON. 273 



the heart along a tube representing an arterial system, the 

 problem assumes a somewhat different form. The rate of flow 

 through the tube must be first ascertained b}^ measuring the 

 discharge from its terminal orifice. This being known, the 

 answer to the question is arrived at by considering what 

 height of column of serum would, if substituted for the heart, 

 be sufficient to determine the same rate of efflux. This can 

 be learnt most accurately by a comparative experiment; it 

 can be deduced approximately from the measurement of the 

 mean pressure actually existing in the aorta. Here, as before, 

 the mechanical work done by the heart is the work which 

 would be required to raise the quantity of serum discharged 

 per second to the height corresponding to the pressure, i. e., 

 to a height something like twelve times that indicated by the 

 mercurial manometer. 



67. Investigation of the Endocardial Pressure in 

 Mammalia. As this mode of investigation can only be prac- 

 tised on animals of large size, and has already perhaps yielded 

 all the results which can be expected from it, it will be suffi- 

 cient to give a cursory account of it here, referring the reader 

 to the papers of its author, Professor Chauveau, for detailed 

 information. The method consists in lodging in one or other 

 of the cavities of the heart of an animal, an India-rubber bag, 

 or ampulla, which communicates by a long narrow tube with a 

 manometer. The introduction of the instrument in question 

 (which has received the name of cardiac sound) into the right 

 cavities through the external jugular vein is perfectly easy, and 

 can be effected in the horse, as I can testify from my own ob- 

 servation, without occasioning the animal the slightest suffer- 

 ing or even inconvenience a fact easily enough understood 

 when we reflect that the internal surface of the vascular system 

 is not supplied with sensory nerves. The ampulla does not 

 come in contact with the surface of the heart. The left ven- 

 tricle is reached through the carotid artery with somewhat 

 greater difficult}'. The left auricle is of course inaccessible. 



The most important results have been obtained by a cardiac 

 sound so constructed that the variations of pressure can be 

 recorded in the right auricle and ventricle simultaneously. By 

 means of this instrument, M. Chauveau has been able to demon- 

 strate the order of succession of the movements of the heart, 

 and the intervals of time which separate them from each other, 

 with an exactitude which would have been otherwise unattaina- 

 ble. Thus he has shown that in the horse the interval between 

 the hardening of the auricle and that of the ventricle is just 

 about a tenth of a second, and that the duration of the ven- 

 tricular systole is about three-tenths, whatever be the number 

 of contractions per minute ; so that frequency of the pulse de- 

 pends not on the time taken by the heart to accomplish each 

 18 



