494 MATERIA MEDICA AND THERAPEUTICS. 



nected with the sympathetic chain ; and that the viscera have 

 also intrinsic ganglia, by which their automatic action is chiefly 

 carried on. 



Sensation. Sensation is a cerebral state, referable to an 

 impression received through an afferent nerve. This generally 

 originates at the periphery, more rarely in the afferent nerve 

 or tract, but is in every case referred to the periphery. In this 

 way an impression (peripheral) becomes a sensation (cerebral), 

 and a sensation in turn may or may not travel onwards into a 

 still higher part of the cerebrum, where it becomes a perception, 

 a part of consciousness, a mental act. Of the various percep- 

 tions, common sensibility alone demands special notice here. The 

 tissues and organs in health are sensitive, but not the seat of 

 actual sensations. Very slight disturbance, however, is suffi- 

 cient to arouse perception or consciousness of the condition 

 of the organs, of which pain is an example, and we therefore 

 assume the constant existence of a quiescent sense, called 

 common sensibility. 



Motion. All movement may be said to originate as an 

 impulse in a nervous centre, whence it is conveyed to muscles 

 or muscular organs by efferent or motor nerves. Thus an 

 impulse arising in the automatic action of the cerebral cells 

 travels from the higher to the lower centres ; here it joins the 

 reflex impulse, proceeding by reflexion from these centres ; 

 and the mixed impulse courses through the motor nerves to 

 a special terminal apparatus, say in a muscle, by which the 

 motor nerve is brought into relation with the organ. Just as 

 a perception in the cerebrum may be referable to a condition of 

 any part of the afferent or sensory side of the nervous system, 

 so muscular contraction may be produced by stimulation of any 

 part of the efferent or motor side, from the convolutions to 

 the muscle itself ; and what is of special interest to the thera- 

 peutist, it frequently originates, wholly or in part, in stimulation 

 of some part of the sensory side, reflected through the 

 centres. 



Consciousness. This in a purely mental state, partly con- 

 sisting of perceptions, and partly inseparably associated with 

 the emotions, the intellect, and the will. Consciousness 

 depends on the perfectness of the whole sensory apparatus, 

 but from a practical point of view it may be considered to 

 reside in the cerebral part of the same, i.e. in the convolutions, 

 where it is readily reached by the therapeutist. 



Sleep. We cannot account perfectly for natural sleep, but 

 we are probably right in associating it with diminished meta- 

 bolism of grey matter, whether due to deficient blood supply, 

 to impaired quality of blood, or to the molecular inactivity of 



