76 



THE PHYSIOLOGY OF MUSCLE AND NERVE. 



groups again falls into smaller divisions according to the kind of 

 activity it excites or inhibits. In the efferent system, for instance, 

 the excitatory fibers may cause contraction or motion if they ter- 

 minate in muscular tissue, or secretion if they terminate in glandu- 

 lar tissue. For convenience of description each of the groups in 

 turn may be further classified according to the kind of muscle in 

 which it ends or the kind of glandular tissue. In the motor group 

 we speak of vasomotor fibers in reference to those that end in the 

 plain muscle of the walls of the blood-vessels; visceromotor fibers, 

 those ending in the muscular tissue of the abdominal and thoracic 

 viscera; pilomotor fibers, those ending in the muscles attached to 

 the hair follicles. The classification that is suggested in tabular 

 form below depends, therefore, on three principles: first, the direc- 

 tion in which the impulse travels normally; second, whether this 

 impulse excites or inhibits; third, the kind of action excited or 

 inhibited, which in turn depends upon the kind of tissue in which 

 the fibers end. 



Efferent 



Afferent 



Excitatory 



Inhibitory 



Excitatory 



Inhibitory j 



Motor 



Secretory 



Inhibito-mo- 

 tor 



In hibi to-se- 

 cretory 



Sensory 



Reflex 



Inhibito-re- 

 flex 



(Motor. 

 Vasomotor. 

 Cardioinotor. 

 Visceromotor. 

 Pilomotor. 

 ( Salivary. 

 J Gastric. 

 ) Pancreatic. 

 < Sweat. 



f Subdivisions corresponding to the varieties of mo- 

 ( tor fibers above. 



\ Subdivisions corresponding to the varieties of se- 

 1 cretory fibers above. 

 V Visual. 

 Auditory. 

 Olfactory. 

 Gustatory. 

 Pressu re. 

 Temperature. 

 Pain. 

 Hunger. 

 Thirst, etc. 



According to the efferent fibers affected. 

 Inhibitory effects upon the conscious sensations are 



not demonstrated. 



The reflex fibers that cause unconscious reflexes 

 are known to be inhibited in some cases at least. 



That the final action of a peripheral nerve fiber is determined 

 by the tissue in which it ends rather than by the nature of the 

 nerve fiber itself or the nature of the impulse that it carries is indi- 

 cated strongly by the regeneration experiments made by Langley.* 

 For instance, the chorda tympani nerve contains fibers which cause 

 a dilatation in the blood-vessels of the submaxillary gland, while 

 the cervical sympathetic contains fibers which cause a constriction 

 of the vessels in the same gland. If the lingual nerve (containing 

 the chorda tympani fibers) is divided and the central end sutured 



* Langley, "Journal of Physiology," 23, 240, 1898; ibid., 30, 439, 1904; 

 "Proceedings Royal Society," 73, 1904. 



