SPINAL CORD AS A PATH OF CONDUCTION. 169 



endogenous fibers, so far as they are ascending, represent afferent 

 paths in which two or more neurons are concerned. The pos- 

 terior root fibers concerned in these paths end in the gray matter 

 of the cord, and thence the conduction is continued by one or 

 more tract cells. The conduction by this set of fibers may be on 

 the same side of the cord as that on which the root fibers entered; 

 or it may be crossed, or, using a convenient terminology, it may 

 be homolateral or contralateral. The endogenous fibers are not 

 a conspicuous feature of the posterior funiculi and little is known 

 of their physiological significance. The physiological value of 

 the exogenous or root fibers in the posterior funiculi has been in- 

 vestigated by a large number of observers. The physiologists have 

 employed the direct method of cutting the funiculi in the thoracic or 

 lumbar region and observing the effect upon the sensations of the 

 parts below the lesion. The positive results of these experiments 

 have been difficult to define. Most of the older observers found 

 that there was no detectable change in the sensations of the parts 

 below, but they paid attention only to cutaneous sensations, and, 

 indeed, chiefly to the sense of pain. Later observers* have differed 

 also in their description of the effects of this operation; but 

 most of them state that the animal shows an awkwardness or 

 lack of skill in the movements of the hind limbs, especially in 

 the finer movements, and this effect is interpreted to mean that 

 there is some loss of muscle sense. This conclusion is strength- 

 ened by the results of pathological anatomy. In the disease 

 known as tabes dorsalis the posterior funiculi of the cord in the 

 lumbar region are affected and the striking symptom of this 

 condition is an interference with the power of co-ordinating 

 properly the movements of the lower limbs, particularly in the 

 act of maintaining body equilibrium in standing and walking, — 

 a condition known as locomotor ataxia. So far as the cutaneous 

 sensations are concerned, — that is, the sensations of touch 

 (pressure), pain, and temperature, — all observers agree that tlie 

 two latter are not affected by section of the funiculi, while regarding 

 touch, opinions have differed radically. Schiff contended that 

 touch sensations are detectable as long as these funiculi are intact, 

 and are seriously interfered with when they are sectioned; but most 

 of the results, pathological and experimental, indicate that when 

 the continuity of these fibers is destroyed, the sense of touch is 

 still present in the parts supplied by the cord below the lesion. 

 An explanation of the confusion in the reported results may be 

 found perhaps in the fact reported below (see p. 174) that fibers 

 conveying the impulses necessary to tactile discrimination pass 

 upward in these funiculi, while other touch (pressure) impulses 



*Borchert, "Archiv f. Phvsiolop;ie," 1902, 389. See also Sherrington, 

 "Journal of Physiology," 14, 255, 1893. 



