166 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



little experimental and not much clinical evidence. Some observers 

 have cut the tract of Flechsig in animals, but with no very obvious 

 effect except again a slight degree of ataxia in the movements 

 below the lesion and some loss of muscular tone.* This result 

 together with the fact that the bundle ends in the cerebellum 

 gives reason for believing that the fibers mediate muscular sensi- 

 bility. As we shall see, much evidence of various kinds connects 

 the cerebellum with the co-ordination of the muscles of the body 

 in the complex movements of standing and locomotion. This 

 power of co-ordination hi turn depends upon the sensory impulses 

 from the muscles, and since the fibers of the tract of Flechsig end 

 in the cerebellum, and since experimental lesion of them gives 

 no loss of cutaneous sensibility and some degree of ataxia, it seems 

 justifiable to conclude that these fibers are physiologically muscle- 

 sense fibers. The tract of Gowers has not been the subject of 

 much experimental study from the physiological side. Clinically 

 the tract may be involved in pathological or traumatic lesions of 

 the lateral columns. Gowers f himself gives a history of some such 

 cases which lead him to believe that this tract constitutes a path- 

 way for pain impulses, and this view or the view that it conducts 

 the impulses of both pain and temperature has been more or less 

 generally accepted. Little confidence, however, can be placed 

 in this conclusion, since the lesions in question were not strictly 

 confined to the column of Gowers. The only positive indication 

 that we have concerning the physiological value of these fibers is 

 given by their histology in the fact that they end for the most part 

 in the cerebellum. The cerebellum we know may be removed in 

 dogs and monkeys without loss of the sensation of pain, tempera- 

 ture, or touch, and this fact speaks strongly against the view that 

 either the tract of Flechsig or that of Gowers is concerned in the 

 conduction of these cutaneous sensations. From a physiological 

 standpoint we should be inclined to believe that both of these 

 tracts conduct the impulses of the deeper sensibilities, particularly 

 the sensations arising from the muscles, tendons, and joints. 

 It would seem, therefore, that all the long ascending tracts in the 

 posterior and lateral columns of the cord may be made up of fibers 

 of muscle sense, using this term in a wide sense to include the deep 

 sensibility of the joints, tendons, and muscles. The immense 

 importance of muscular sensibility in the maintenance of life and 

 in defense against enemies may explain, upon the doctrine of the 

 struggle for existence, why the long paths should have been devel- 

 oped first in connection with this sense. 



*Bing, " Archiv fur Physiologie, " 1906, 250. 

 t Gowers, " Lancet," 1886. 



