162 



THE CIRCULATION OF THE BLOOD AND LYMPH 



ductivity of the heart. Thus in the frog's heart during stimulation of 

 the vagus, the contraction passes more slowly, and during stimulation 

 of the sympathetic more quickly, from auricles to ventricle. 



In mammals (and in what follows we shall restrict ourselves chiefly 

 to the dog, cat, and rabbit, as it is in these animals that the subject 

 has been most carefully studied) the inhibitory fibres run down the 

 vagus in the neck and reach the heart by its cardiac branches. They 

 are derived from the bulbar roots of the spinal accessory, whose inner 

 branch joins the vagus. The augmentor fibres leave the spinal cord in 

 the anterior roots of the second and thira thoracic nerves, and possibly 

 to some extent by the fourth and fifth. Through the corresponding 



Fig. 736- Miniature Myocardiograph (actual size) 

 (Wiggers). C, light. aluminium. segment capsule 

 covered by tightly stretched rubber dam, upon 

 which is cemented an aluminium plate pivoting 

 upon the chord side of the capsule. The plate 

 carries a light arm, A, with an eyelet at its end. 

 A similar arm, A 1 , is rigidly fastened to the body 

 of the capsule. The arms can be bent so that 

 the distance between the eyelets varies from 

 3 to 25 millimetres, and are connected by 

 stitches through the eyelets to points on the 

 auricular surface. The approximation of the 

 points causes a negative pressure in the cap- 

 sule, and in the recording capsule (see descrip- 

 tion of Fig. 31, p. 93) connected with it by the 

 tube T. Hence, the down-stroke of the^curve 

 represents contraction, the up-stroke relaxation. 

 The apparatus is supported by a very', light 

 spring, S. This enables it to follow varying 

 degrees of distension and movement of the 

 auricle without affecting the curve of contrac- 

 tion. The small mass (less than 2 gm.)'and 

 high vibration frequency of the instrument 

 insure a more faithful record of the con- 

 traction than with older forms. 



white rami communicantes they reach the sympathetic cord, and 

 running up through the stellate ganglion (first thoracic), and the 

 annulu* of Vieussens, which surrounds the subclavian artery, to the 

 inferior cervical ganglion, they pass off to the heart by separate ' acce- 

 lerator ' branches, taking origin either from the annulus or from the 

 inferior cervical ganglion. Some augmentor fibres are often, if not 

 always, present in the dog's vago-sympathetic in the neck. It is 

 especially easy to demonstrate their presence five or six days after 

 section of the nerve, when the excitability of the inhibitory fibres has 

 disappeared. 



In the dog the vagus and cervical sympathetic are, in the great 

 majority of cases, contained in a strong common sheath, and pass 



