284 



FUNCTIONS OF NUTRITION. 



apparatus, first employed by Marey.* The apparatus is composed of 

 two parts ; first, an instrument introduced into the cardiac cavities, to 

 receive and transmit their variations of pressure ; and secondly, a reg- 

 istering machine, by which these variations are permanently recorded. 



The first instrument consists of two slender parallel tubes, of such 

 length that, when introduced into the jugular vein of the horse, one 

 will reach the cavity of the right auricle, the other that of the right 

 ventricle. The lower extremity of each tube is widely fenestrated and 

 covered with an elastic membrane, to receive the pressure of the blood 

 in the cardiac cavity. The upper extremity is connected by a flexible 

 tube with a shallow metallic cup or drum, also covered with an elastic 

 membrane. By this means the pressure of the blood within the auricle 

 or ventricle is communicated to the corresponding external drum. Upon 

 each drum rests a light lever, in such a way that any increased pressure 

 within the drum, which distends its elastic membrane, lifts at the same 

 time the farther end of the lever. Consequently the oscillation of the 

 two levers indicates the variations of pressure within the auricle and 

 ventricle respectively. 



The registering machine consists of a revolving cylinder or strip of 

 paper, moving by clockwork at a uniform rate, with which the extremi- 

 ties of the levers are in contact, and upon which they trace correspond- 



FIG. 65. 



ECA 



CA.RDIOGRAPHIC TRACE, showing variations of pressure during cardiac pulsations in the right 

 auricle and right ventricle of the horse. J2 A. Tracing of right auricle, o, o, o. Maximum of 

 pressure in auricular cavity. R V. Tracing of right ventricle, x, x, x. Maximum of pressure 

 in ventricular cavity. (Marey.) 



ing lines. When the pressure in either cardiac cavity is uniform, its 

 lever will trace upon the revolving cylinder a straight line ; but when- 

 ever this pressure is increased the line will rise above the horizontal, 

 and when it is diminished the line will sink to a corresponding level. 

 The upward and downward slopes of the two tracings will therefore 

 record the time, rapidity, force, and duration of all changes in pressure 

 in the right auricle and right ventricle of the animal under observation. 

 The tracings obtained by this method (Fig. 65) show that the con- 

 traction of the auricle precedes by a very short interval that of the 



*Physiologie Medicale de la Circulation du Sang. Paris, 1863, p. 54. 



