384 THE NERVOUS SYSTEM. 



impression may be conducted through the spinal cord to the 

 brain, where the mind may perceive it. In the opposite direc- 

 tion, mental influence may be conducted from the brain through 

 a succession of nervous centres the spinal cord and ganglia, 

 and one or more ganglia of the sympathetic to produce the 

 influence of the mind on the digestive and other organic func- 

 tions. In short, in all cases in which the mind either has 

 cognizance of, or exercises influence on, the processes carried 

 on in any part supplied with sympathetic nerves, there must 

 be a conduction of impressions through all the nervous centres 

 between the brain and that part. It is probable that in this 

 conduction through nervous centres the impression is not prop- 

 agated through uninterrupted nerve-fibres, but is conveyed 

 through successive nerve-vesicles and connecting nerve-fila- 

 ments ; and in some instances, and when the stimulus is ex- 

 ceedingly powerful, the conduction may be effected as quickly 

 as through continuous nerve-fibres. 



But instead of, or as well as, being conducted, impressions 

 made on nervous centres may be communicated from the fibres 

 that brought them, to others; and in this communication may 

 be either transferred, diffused, or reflected. 



The transference of impressions may be illustrated by the 

 pain in the knee, which is a common sign of disease of the hip. 

 In this case the impression made by the disease on the nerves 

 of the hip-joint is conveyed to the spinal cord ; there it is trans- 

 ferred to the central ends or connections of the nerve-fibres 

 distributed about the knee. Through these the transferred 

 impression is conducted to the brain, and the mind, referring 

 the sensation to the part from which it usually through these 

 fibres receives impressions, feels as if the disease and the source 

 of pain were in the knee. At the same time that it is trans- 

 ferred, the primary impression may be also conducted ; and in 

 this case the pain is felt in both the hip and the knee. So, not 

 unfrequently, if one touches a small pimple, that may be seated 

 in the trunk, a pain will be felt in as small a spot on the arm, 

 or some other part of the trunk. And so, in whatever part of 

 the respiratory organs an irritation may be seated, the impres- 

 sion it produces is transferred to the nerves of the larynx ; and 

 then the mind perceives the peculiar sensation of tickling in 

 the glottis, which best, or almost alone, excites the act of cough- 

 ing. Or, again, when the sun's light falls strongly on the eye, 

 a tickling may be felt in the nose, exciting sneezing. In all 

 these cases, the primary impression may be conducted as well 

 as transferred ; and in all it is transferred to a certain set of 

 nerves which generally appear to be in some purposive rela- 

 tion with the nerves first impressed. 



