982 CUTANEOUS SENSATIONS. 



channel leading in common from visceral and from cutaneous afferents. 

 To Head we owe the knowledge that the spatial arrangement of the 

 radiation is, largely at least, of segmental character. Each viscus stands 

 in relation with a definite patch of skin. The patches thus marked out 

 do not correspond with any of the areas of distribution of the peripheral 

 nerves, as far as known to gross human anatomy, but resemble and 

 in fact strikingly agree in disposition with the segmental skin areas, 

 found to belong to the spinal nerve roots, i.e. spinal ganglia. The 

 segmental character of the "reference," and the likelihood that the 

 connection or communication occurs where the column cell is inter- 

 calated, that is, at the synapse in the conduction chain, both suggest 

 that the seat of " reference " is in the spinal grey matter itself. 



The spinal ganglia contain, of course, the afferent visceral nerve fibres of 

 the white rami and also the afferent nerve fibres from the skin, etc. Regard- 

 ing the manner and place of "radiation," Miiller, as early as 1834, wrote, 

 " either of two hypotheses may be adopted." The radiation may occur in the 

 spinal ganglion, by escape there of excitement from one nerve cell to another, 

 the conductors being there no longer isolated by protective sheaths. Or, " the 

 sympathetic sensations are the result of the radiation of the irritation from the 

 fibres primarily affected upon the roots of other fibres in the brain or spinal 

 cord, just as in the production of reflex movements impulses conveyed by 

 sensitive nerves into the cord are communicated to motor nerves ; the only 

 difference being that, when sympathetic sensations are produced, the radiation 

 of the impulses does not reach motor but only sensory fibres, or, at any rate, 

 acts on sensory at the same time as 011 motor nerves." " This is another 

 proof that the same sensation is produced at whatever point of its length 

 a nerve fibre is irritated." The mere radiation of an impulse will therefore 

 suffice to produce sympathetic sensations. " The extension of irritation in the 

 spinal cord, from the roots of the sensory to the roots of the motor nerves, and 

 the fact that sensory nerves without ganglia, e.g. optic in the instance where 

 a strong light causes a sensation of tickling in the nose exhibit radiation of 

 sensations, shows that the radiation must take place not in the ganglia but in 

 the central nervous system." x The seat of radiation is considered by Head also 

 to be intraspinal, by Kyri, 2 however, to be intraganglionic. As above stated, 

 I myself should regard it as at the site of synapsis between the visceral spinal 

 ganglion cells and column cells of the grey matter that continue the thermal- 

 gesic chain of conduction. The referred sensation is not one of touch, but of pain, 

 is, in fact, a " sympathy." The segmental patch of skin to which the reference 

 is made may be hyperalgesic ; generally, not the whole of it, but a part, is also 

 hypersesthetic to warmth; this is called by Head "the maximal point." In 

 fact, the visceral part of the spinal segment communicates its own excitement 

 to a certain portion of the somatic part of the segment. Thus Head finds that 

 disease of the kidney and ureter cause reference of pain and hyperalgesia in 

 skin, the sensory innervation of which is from the tenth, eleventh, and twelfth 

 thoracic spinal ganglia. Similarly with disease of the cardiac end of the 

 stomach and the skin fields of the sixth and seventh thoracic spinal ganglia. 

 But not all spinal segments innervate viscera. Several neither give fibres to 

 nor receive fibres from the viscera, that is, possess no white ramus com- 

 municans. It is especially in the limb regions that the visceral component of 

 the spinal segment is wanting. Head finds no referred pains in the fifth, 

 sixth, seventh, and eighth cervical, nor in the second, third, or fourth lumbar 

 segments. The afferent nerves of the viscera compose to a certain extent a 

 twofold system, a cranial and a spinal, the former being the vagus, the latter 



1 "Elements of Physiology, " translated by W. Baly, London, 1837, vol. i. 



2 Centralbl. f. Gfyiuik., Leipzig, 1894; and Vcrsamml. deutsch. Naturf., etc., Wien, 1894. 



