THE SPINAL CORD. m 515 



The current views regarding the physiologic activities of the afferent 

 portion of the peripheral nerve system and its relation to the production of 

 different forms of sensibility have been enlarged by the results of the investi- 

 gations that have been made by Head. Thus, he has shown that the afferent 

 nerves consist of three systems, each of which when excited to activity evokes 

 in consciousness a different and distinct group of sensations as follows : 



1. One group of nerves which when stimulated evoke sensations through 



which is gained the power of cutaneous localization, of the discrimina- 

 tion of two points of a compass, of the finer grades of temperature, and 

 of light touch. To this form of cutaneous sensibility the term epicritic 

 has been applied. 



2. A second group of nerves which when vigorously stimulated, as by the 



prick of a pin or by the application of a hot or cold object, evoke sensa- 

 tions of pain or heat and cold. To this form of cutaneous sensibility 

 the term protopathic has been applied. This form of sensibility is 

 unaccompanied by a definite appreciation of the locality stimulated for 

 the reason that the stimulus causes a widespread or radiating sensation 

 which at times is referred to parts far removed from the part stimulated. 



3. A third group of nerves which when stimulated evoke sensations of pres- 



sure, of the passive position and the movements of parts of the body, and 

 sensations of pain as well, if the stimulus (pressure) be severe, or if the 

 underlying structures are injured, e.g., the rupture of a joint. The 

 nerves subserving this form of sensibility are contained in the trunks 

 of the motor (muscle) nerves and are distributed to muscles, tendons 

 and joints. To this form of sensibility the term deep has been applied. 

 As previously stated, the pathways in the spinal cord for the transmission 

 of afferent nerve impulses are imperfectly known, and for their determina- 

 tion in human beings reliance must be placed on observations of the results 

 of disease of the cord, supplemented by experiments made on the cord in 

 mammals such as monkeys and apes. 



From the classification of the various forms of sensibility by Head, the 

 following table showing the effects or symptoms following a transverse lesion 

 of one-half of the cord in man has been constructed by Turner and Stewart. 



SCHEME SHOWING THE BROWN-SEQUARD ' 'SYMPTOM-COMPLEX/' 



BASED ON HEAD'S OBSERVATIONS. 

 Side of lesion. Side opposite lesion. 



Motor paralysis. No paralysis. 



Retention of tactile, light pressure, Tactile and light pressure sensibili- 

 painful, and thermal sensibilities. ties may or may not be impaired. 



Painful and thermal sensibilities 



abolished. 



Painful pressure retained. Painful pressure abolished. 



Impairment or abolition of tactile Retention of sense of position and 

 discrimination, and sense of posi- of tactile discrimination, 

 tion of limbs. 



Retention of cutaneous localiza- Cutaneous localization depends up- 

 tion. on the state of tactile sensibility. 



