1897.] Psychology. 1059 
disease of the peripheral sensory neuron make the assumption of peri- 
pheral pain nerves and sense organs one that stands closely related to 
the facts. 
“There is a specialized pain tract in the spinal cord which is cer- 
tainly constituted in part by the gray column, and which may be com, 
posed of a part of the gray column on both sides, including the com- 
missure and a part of the lateral tract. Into this pain tract, nerves 
from the sympathetic system and from the internal organs, together 
with all specialized nerves from the periphery, discharge their stimu- 
lation when this is relatively intense. The intensity necessary to bring 
about this discharge may be that which is sufficient to overcome the 
resistance offered by the tract. This tract passes up through the optic 
thalamus and posterior limb of the internal capsule, the ‘carrefour 
sensitif, into the cerebrum, and reaches some region unknown, but 
probably a part of the somesthetic area. This hypothetical region of 
the somesthetic area may be looked upon as the pain centre. 
“ There is some warrant of justification for considering the pain tract 
in the spinal cord as the spinal nerve organ of pain, which, together 
with the hypothetical specialized cortical centre, constitutes the specific 
organ of pain. Any part of this central pain organ may be stimulated 
‘in the cortex or below it, either by stimuli discharging into it through 
normal physiological processes, by spinal or cortical association, by 
irritation due to disease, and perhaps by a vascular disturbance within 
the central nervous system. 
“Thus pain may be a sensation of purely central nervous origin. 
The arousal of pain by stimuli and its presentation in consciousness 
along with other sensations may be explained by the simultaneous 
association of pain with other forms of stimulation—an association that 
may take place at any level of the nervous system. When such asso- 
ciation takes place in the cortex, we have conscious association, the 
sangre of pain with other sensations, with percepts, or with ideas.” 
ei The universality of pain association with sensations of 
sees intensity is explainable anatomically and physiologically by 
the discharge of intense stimuli carried by all peripheral nerves into 
the central pain organ: that this central pain organ has no peripheral 
nerves of its own, possessing a specific pain function and no other, can 
receive satisfactory explanation only from biological considerations of 
the significance of pain as a warning against dangerous stimuli of the 
environment. This fact would suggest an early phylogenetic develop- 
ment of a pain sense in the organism ; in fact, the pain sense may have 
been the first of all the special senses.” * 
5 Op. cit., pp. 940-941. 
