148 THE CIRCULATION OP THE BLOOD 



cut away at one end Avhich is 3 ram. in diameter and covered with rubber dam. By 

 adjustment of this stopcock the pulsations of the fluid in A and B can be damped to 

 a greater or less extent before they are transmitted into the segment capsule. A small 

 piece of celluloid carrying a tiny mirror rests on the rubber dam, being pivoted on the 

 chord side of the capsule. A mirror is attached to the capsule with its plane so ad- 

 justed that the image of a strong light placed at some distance from it is focused on the 

 little mirror carried by the celluloid. The ray reflected from the little mirror and 

 again reflected from the larger mirror is adjusted so as to impinge upon a moving 

 photographic plate travelling at a uniform rate in a suitably constructed photographic 

 apparatus. By the use of such an apparatus the chief errors encountered by the use 

 of the older instruments are eliminated, because there is no moving mass of fluid and 

 there are no levers to set up spurious vibrations. Curves secured by the use of this 

 instrument are shown in Fig. 33. 



Fig. 33. Optical records of intraventricular pressure; a-b, auricular systole; b-d, presphygmic 

 period; d-f, sphygmic period; after /, diastole. Instruments of varying degrees of sensitiveness 

 were employed in taking the curves. ('From Wiggers.) 



Two objects must be kept in view in analyzing the curves: (1) Curves 

 obtained from the different cavities may be compared in order to de- 

 termine the exact moment during the cardiac cycle at which such pres- 

 sure changes occur as must serve to produce opening or closing of the 

 various valves; and (2) the contour of the curves obtained from each 

 cavity may be examined in order to find out exactly how the pressure 

 in that particular cavity is behaving. 



Comparison of the Curves 



Before using the curves for ascertaining the relative pressure in the 

 different cavities, they must be graduated according to some scale, for 

 it is clear that by the use of instruments like those we have been describ- 

 ing, the absolute pressure value of each curve will vary according to the 

 construction of the instrument (thickness of membrane, etc.), and in- 

 deed instruments of varying degrees of resistance must be employed in 

 taking curves from places having such different pressures as exist in 

 the auricles and ventricles. The graduation is, however, a very easy 

 matter, and consists, as already explained (page 128), in connecting the 



