MUSCULAR SENSATION. 403 



fibres of the spindle in either or all of three different modes (Fig. 199): 1. 

 The axis-cylinder may flatten out and twine in rings and spirals about the 

 muscle-fibre. 2. The axis-cylinder may break nj> into a number of leaflets 

 applied to the muscle-fibre (secondary mode). :]. The axis-cylinder may 

 end in a plate of varicose fibrils resembling the motor end-plate. 



When we consider that it is through muscular sensation that we derive our 

 most accurate conceptions of the form, weight, and position of objects, and through 

 which we explore our own body-surface and distinguish its areas of localization ; 

 that this is the fundamental sense by which the sensations arising in most 

 other organs are tested and verified ; and that it is from the sense of muscular 

 movement that we can form ideas of time and space, — it may well be regarded 

 as the mother of all sense-perceptions. Normal muscles, even when function- 

 ally inactive, are still in a state of tonic contraction ; it is not improbable that 

 this tone is a reflex action whose sensory element is formed by the impulses 

 travelling along nerves of muscular sensation. Such impulses are probably 

 indispensable to the preservation of the equilibrium of the body. 



Sherrington found that if he separated the aponeurosis belonging to the 

 distal portion of the vastus medialis muscle, under which the muscle-spindle- 

 are numerous, the knee-jerk could no longer be excited through the muscle. 



Our appreciation of the weight of bodies is determined by lilting them. 

 But even in so simple an exercise of the muscular sense as this the judgment 

 is subject to extraordinary illusions depending on the preconception of the 

 weight of a body, and consequent muscular effort put forth in lifting it. 

 When bodies having the same weight and size, such as appropriately loaded 

 pieces of iron, cork, and wood, are compared, the specifically lighter body will 

 seem to be heavier. "Before lifting an object we normally estimate the 

 approximate weight by sight, and the effort to be exerted in lifting is adjusted 

 semi-automatically upon the basis of this preliminary estimate. If insufficient 

 effort is put forth at the beginning of the lifting, the weight of the object will 

 be overestimated. If too great effort is put forth, the weight of the object 

 will be underestimated." 1 In comparing the weight of objects having 

 different sizes the illusion takes another direction. Thus an inflated paper 

 bag may be estimated to have the same weight as a piece of lead weighing 

 sixty times as much." 



The clinical study of disease in the central nervous system affords strong 

 evidence of the functional independence of the sense organs involved in the 

 appreciation of touch, heat, cold, and pain. In certain diseases of the spinal 

 cord, areas of skin may be mapped out in which sensations of pressure are 

 lost, but those of temperature remain, and vice versd. In other diseases the 

 patient can appreciate warmth applied to the skin, but not cold. 



The sensations of cold and pressure seem to be usually lost or retained 

 together, while those of warmth and pain have a similar connection. It is a 

 peculiar fact that sometimes in the early stages of ether and chloroform narco- 

 sis the sense of touch remains while that of pain is abolished. Funke 3 refers 



'Seashore: Op. rit. 'Wolfe: Paycholoc/iml Rivim; ISDN, p. 25. 



8 " Der Tastsinn," Hermann's Handbuch der Phyaiologie, Bd iii. 8. 2. 



