324 RESPIRATION. 



periods during which the diaphragm remains in the position 

 assumed by it at the close of ordinary expiration. To record 

 the effects graphically, any of the methods recommended in 

 the preceding paragraphs may be used. If the method de- 

 scribed in 99 is employed", a tracing is obtained which 

 exactly resembles fig. 255. The tracing, fig. 256, 1 was drawn 

 by inserting a bag between the diaphragm and the liver. 



SECTION VI. INFLUENCE or THE RESPIRATION ON THE CIRCULATION. 



105. If the stethoscope is applied to the praecordia of a dog, 

 it is easily observed, especially if the animal has been narco- 

 tized, that the rate at which the contractions of the heart 

 succeed each other is subject to rhythmically recurring varia- 

 tions, and that the acceleration follows eath expansion of the 

 chest, lasting during the first part of the succeeding expiration ; 

 while during the latter part of the expiratory period the 

 period during which, as we have seen, air is expelled very 

 slowly the diastolic intervals become longer. These facts 

 admit of much more precise demonstration by the graphic 

 method. For this purpose the most convenient instrument is 

 that shown in fig. 257. 



It is a kymograph so constructed as to record the arterial 

 pressure and respiratory movements simultaneously. The 

 mercurial manometer consists of two limbs of equal length, 

 one of which, the distal (A), is much wider than the other 

 near the top, the relation between the lumen of the one and 

 that of the other being 1:10. The float which rests on the 

 distal column is of boxwood. Its under surface is concave, so 

 as to fit the convex surface of the mercury. By the vertical 

 rod it is connected with a light lever, i>, about two feet in 

 length, which is counterpoised by a weight suspended to it on 

 the other side of the brass bearing, E. At its thin end, the 

 lever carries a pen, the distance of which from D is such, that 

 for every inch of variation of difference between the two col- 

 umns of the manometer, it rises or falls three-tenths of an 

 inch. It will be readily understood that the movement of the 

 pen, instead of being rectilinear, is circular; consequently, it 

 is vertical only when the lever is horizontal ; for which reason 

 the fulcrum, E, which is so constructed as to slide up and down 

 on the brass uprights, must always be placed in such a posi- 

 tion that the lever is horizontal. The height of the mercurial 



1 The tracing, fig. 256, shows that during the whole period of excita T 

 tion the diaphragm remained motionless in the position of expiration, 

 with the exception that at gradually lengthening intervals it executed 

 momentary contractions. When, after the cessation of excitation, the 

 respiratory movements were resumed, they were slower 'but more ex- 

 tensive than before. 



