99o CUTANEOUS SENSATIONS. 



regarding the mechanical irritations employed, which might detract from their 

 efficiency as excitants, namely — (1) The thoroughly abnormal character of the 

 production of the strains in many cases, e.g. tvvistings, foldings, etc., which 

 the body itself cannot produce ; (2) the absence of the opportunity for pro- 

 longed summation. Against such negative evidence is the fact that muscles 

 stretched passively for a prolonged time become painful, 1 and that the passive 

 stretching of muscle is a most efficient excitant for normal spinal reflexes 

 through its afferent nerves. 2 It would appear that only mechanical conditions, 

 akin to such as obtain in muscles during their functional activity, can initiate 

 from them sensation and pain. The structure of muscle spindles certainly 

 points to the adequate stimulus being of a mechanical kind, 3 and that of 

 tendon organs points in the same direction. 



Extreme and abnormal actions of muscles furnish the best 

 instances of muscular pain. Weber 4 felt the muscles of his horizontally 

 held arm become painful in 300 seconds, unbearably so in 900 seconds. 

 At the same time contractions as vigorous as those of cramp may be 

 caused without the painful sensation of cramp. 5 To attribute the sensa- 

 tion of cramp merely to compression of sensory nerves passing through 

 the muscles, and not to sensory nerves of their own, is certainly not 

 permissible. The pain of muscular cramp is distinctly perceived to 

 be in the contracting muscles, that is, is referred to the contracting 

 muscles. The adequate stimulus seems under certain circumstances — 

 and among these excessive duration appears eminently important — to 

 elicit pain from the muscular sense. A specific set of nerve fibres 

 and end organs, devoted solely to production of pain, although to 

 the above extent supported by analogy from the skin, does not appear 

 a warrantable postulate for muscles. 



The feeling of muscular fatigue is a form of common sensation that has 

 undoubtedly considerable "negative tone." It presents, in accordance Avith its 

 amount, practically infinite shades from the scarcely unpleasant up to the 

 extremity of distressful. It is a state certainly largely due to the regularly 

 employed specific nerves of muscular sense. In its relation to them it is well 

 comparable with the feeling of hunger in relation to the visceral nerves. 



The viscera offer still another field for analogy. There we find 

 regions of the body, usually only in very subordinate degree sensifacient, 

 that under certain circumstances evoke extremity of pain. The impulses 

 embouching vid the vagus and afferent spinal roots from the visceral 

 nerves upon the central nervous system appear hardly at all to elicit 

 ordinarily conscious reactions. When abnormally they do so, they 

 seem almost invariably to produce pain as their result. It is as 

 though particular afferent nerves, which usually are not in the strict 

 meaning of the term sensory nerves at all, can on occasion become 

 " sensory," even to the extent of convulsing the whole mind. Some 

 authorities, as above mentioned, teach that the visceral nerves are 

 generating constantly "obscure sensations." 6 It would rather seem 

 that these nerves intermittently with phasic regularity launch sensory 

 impressions (as well as viscero-motor, secreto-motor, and other 

 reflexes) that do not trouble the stream of consciousness at all. These 



1 Cf. E. H. Weber, op. cit. ; also, Scliiff, "Muskel- u. Nervenphysiologie," Lahr, 1858. 



2 Sherrington, Proc. Hoy. Soc. London, 1893, vol. lii. 



3 Sherrington, Journ. Physiol., Cambridge and London, 1894, vol. xvii. ; and C. Huber, 

 Journ. Gomp. Neurol., 1898, vol. viii. p. 169. 



4 Op. cit. s Vulpian, "Lecons sur la physiol. du systerue nerveux," Paris, 1866. 

 G See Vulpian, op. cit.; Foster, "Text-Book of Physiology," London, 1891, part iv. 



