518 Dynamic Theory. 



is stimulated the first effect is a check or stoppage of the beating of the 

 heart. The last one is the accelerans, so called because when it is stim- 

 ulated the heart moves faster. In regard to the inhibitory nerve it ap- 

 pears that it is not inhibitory in the long run ; ' ' but that it ultimately 

 improves the condition of the heart as regards force, rate, or regularity 

 one or all of these ; " so G-askell, the best authority on the sub- 

 ject, regards it as a true "anabolic nerve. " The roots of the vagus nerve 

 are in the medulla oblongata, and here there is a mass of nervous mat- 

 ter which is a center of sensation for the visceral parts of the body. 

 The vagus nerve is both motor and sensory, and this center is the organ 

 for receiving the sensory reports of the state of the viscera and various 

 other organs, and reflecting them to motor organs with which they are 

 related, among which is especially ^the heart. When certain organs 

 served by the vagus nerve are in a condition to need more blood, the 

 current up the sensory nerve from such organs to the center in the 

 medulla is such that it excites the so-called inhibitory nerve, down which 

 a stimulus goes to the heart. This organ then works a little harder and 

 so furnishes the lacking aliment. ( It may be that the stimuli used in 

 the experiments on the inhibitory nerve were too strong for it and dazed 

 the heart at first, as the eye is dazzled by a too sudden avalanche of sun- 

 light from which it, however, soon recovers. ) The accelerans nerve prob- 

 ably acts for some other organs to stimulate the heart in their behalf. 

 Of these two classes of nerves Dr. Ferrier says : ' ' The inhibitory nerves 

 may be stimulated and the heart restrained by powerful irritation of the 

 sensory nerves of the surface generally, by irritation of the sensory 

 branches of the fifth in the nostrils, by irritation of the sensory nerves 

 of the larynx ; and in particular by irritation of the intestinal sensory 

 nerves. Thus a smart tap on the intestines of a frog causes the heart to stop, 

 a fact which serves to explain the danger of blows on the epigastrium, 

 and the fatal consequences which, in certain conditions of the system, 

 sometimes follows the sudden shock of a large draught of cold water or 

 irritant poison on the sensory nerves of the stomach. The accelerator 

 nerves can be excited reflexly by stimulation, among others, of the af- 

 ferent nerves of the muscles, a fact which may partlv have to do with 

 the increased rapidity of the heart's action during active muscular 

 exertion." Dr. Brunton thinks the inhibition is due to the interference 

 of molecular vibrations by the different nerve currents. 



During active muscular exertion it is shown that the blood vessels of 

 the muscles become distended and have a greater quantity of blood in 

 them. There is a nerve center in the medulla oblongata called the vaso- 

 motor center. It is the starting point for the motor nerves which sup- 

 ply the blood vessels of the arterial system. These vessels are simply 

 tubular muscles, and when a large number of them are stimulated, their 



