164 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



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 physio- 

 logical value of the ascending fibers in the posterior columns has been 

 investigated by a large number of observers. The physiologists 

 have employed the direct method of cutting the columns in the 

 thoracic or lumbar region and observing the effect upon the sensa- 

 tions of the parts below the lesion. The positive results of these 

 experiments have been difficult to interpret. Most of the older 

 observers found that there was no detectable change in the sensa- 

 tions 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 columns 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 move- 

 ments 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 con- 

 cerned, that is, the sensations of touch (pressure), pain, and tem- 

 perature, all observers agree that the two latter are not affected, 

 while regarding touch opinions have differed radically. Schiff 

 contended that touch sensations are detectable as long as these 

 columns 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. To summarize, therefore, we may say that the evidence 

 at hand proves that the ascending fibers of the posterior column 

 do not convey impulses of pain or temperature, that if they convey 

 any touch (pressure) impulses they certainly do not form the only 

 path of conduction for this sense, and that most probably their 

 chief function is the conduction of impulses of muscle sense, 

 that is, they consist of sensory fibers from the voluntary muscles. 

 The muscle sensations thus aroused in the higher parts of the 

 brain are necessary to the proper co-ordination of the movements 

 of the muscles. Injury to these columns, therefore, while it does 

 not cause paralysis, is followed by disorderly that is, ataxic 



* Borchert, "Archiv f. Physiologic," 1902, 389. See also Sherrington, 

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



