DIVISION OF THE PNEUMOGASTRICB. 231 



Experiments on the influence of the sympathetic nerves 

 upon the heart are not quite as satisfactory as we might 

 desire. Brachet asserts that the action of the heart is imme- 

 diately arrested by destroying the cardiac plexus. 1 With 

 regard to this observation, we must take into account the 

 difficulty of making the operation, and the disturbance of the 

 heart consequent upon the necessary manipulations ; circum- 

 stances which take away much of its value. It has been 

 shown pretty conclusively, however, that stimulation of the 

 sympathetic in the neck has the effect of accelerating the 

 pulsations of the heart. 2 The extreme difficulty of dividing 

 all the branches of the sympathetic going to the organ leaves 

 a doubt as to whether such an operation would definitely 

 abridge its action. 



We have next to consider the influence of the pneumo- 

 gastrics upon the heart. Experiments on these nerves are 

 made with greater facility than on the nerves of the sympa- 

 thetic system, and the results are much more satisfactory. 

 Like all the cerebro-spinal nerves, the influence generated 

 in the nervous centre from which they take their origin 

 is conducted along the nerve, and manifested at its distribu- 

 tion. When they are divided, we may be sure that, as far 

 as they are concerned, all the organs which they supply 

 are cut off from nervous influence ; and when galvanized in 

 their course, we'imitate or exaggerate the influence sent from 

 the nervous centre. 



The invariable effect on the heart of division of the pneu- 

 mogastric nerves in the neck is an increase in the frequency, 

 and diminution in the force, of its pulsations. One or two 



has been known to produce this effect. In fine, this may be done by any exten- 

 sive injury to the nervous system ; but this fact does not teach us much with 

 regard to the physiological influences of the nerves. For example, while crush- 

 ing of the brain arrests the heart, the brain may be removed from a living animal, 

 and the heart will beat for days. Experiments upon the influence of the medulla 

 oblongata and spinal cord are by no means satisfactory. 



1 Cyclopcedia of Anatomy and Physiology, vol. ii., p. 612. 



2 MILNE-EDWARDS, Physiologic, tomeiv., p. 156, note. 



