THE SPINAL CORD 545 



which are reached by the upward coursing of some of the dorsal root fibers 

 through the columns of Goll and Burdach. They are then transmitted by 

 the internal arcuate fibers and the fillet either directly or indirectly to the 

 cortex of the cerebrum and translated into conscious sensations. The sensa- 

 tions thus arising may be divided into x special and general sensations. Of 

 the former may be mentioned the sensations of temperature, pain, touch, 

 pressure, passive position and movements of parts due to the activity of 

 skeletal muscles; of the latter may be mentioned hunger, thirst, fatigue, 

 well-being, etc. 



Though all the impulses that give rise to *these varied sensations are 

 contained within the fibers of the afferent peripheral nerves, they are on 

 reaching the cord distributed by the intraspinal mechanisms to different 

 tracts of nerve-fibers, each of which transmits to localized areas of the cerebral 

 cortex, the somesthetic areas, a special group of impulses which give rise to 

 sensations of various kinds such as those just mentioned. 



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 system 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 system 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 system 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. 

 The pathways through the spinal cord that conduct these afferent im- 

 pulses to the brain are ill-defined and imperfectly known, and only for a few 

 sensations can it be said that their pathways have been determined. The 

 reason for this obscurity lies partly in the difficulties of experimentation, 

 partly in the difficulties of interpretation. Clinical observations are for 

 special reasons more or less untrustworthy. 



As the outcome of many investigations it may be said that a^transverse 

 section of one lateral half of the cord in the monkey, or a lesion involv- 

 ing the one lateral half in man, as a rule abolishes many if not all forms of 

 cutaneous sensibility on the opposite side below the injury. This would seem 



