THE SENSES. 



seems to be mud) in favor of all of these views. The weight of evi- 

 dence is, however, rather against there being any special pain sense with 

 a special end-organ and fibres. It is, however, certain that even if any 

 variety of pain be a special sensation, some kind of pain may be pro- 

 duced by stimulation of the bare sensory nerves apart from any special 

 form of nerve termination. It is said that the main difference between 

 the common sensation which tells us of the condition of all parts of the 

 body and of which thirst and hunger are but examples, the one inform- 

 ing us of the condition of the palate and the other of the state of our 

 stomach, and the special sense of touch and temperature, is that the 

 latter are provided with special apparatus. By means of this apparatus 

 we are able to localize the sensation from which it is possible to form 

 judgments. Such a special apparatus is evidently not absolutely essen- 

 tial for the sensation of pain, but this does not exclude the idea that 

 pain may result from over-stimulation of a nerve of special sense or of 

 its termination. 



The Muscular Sense. The estimate of a weight is usually based 

 on two sensations: 1, of pressure on the skin, and 2, the muscular sense. 

 The estimate of weight derived from a combination of these two 

 sensations (as in lifting a weight) is more accurate than that derived 

 from the former alone (as when a weight is laid on the hand) ; thus 

 Weber found that by the former method he could generally distinguish 

 19| oz. from 20 oz., but not 19f oz. from 20, while by the latter he could 

 at most only distinguish 14| oz. from 15 oz. 



It is not the absolute, but the relative, amount of the difference of 

 weight which we have thus the faculty of perceiving. 



It is not, however, certain, that our idea of the amount of muscular 

 force used is derived solely from the muscular sense. We have the 

 power of estimating very accurately beforehand, and of regulating, the 

 amount of nervous influence necessary for the production of a certain 

 degree of movement. When we raise a vessel, with the contents of 

 which we are not acquainted, the force we employ is determined by the 

 idea we have conceived of its weight. If it should happen to contain 

 some very heavy substance, as quicksilver, we shall probably let it fall; 

 the amount of muscular action, or of nervous energy, which we had 

 exerted being insufficient. The same thing occurs sometimes to a, person 

 descending stairs in the dark ; he makes the movement for the descent 

 of a step which does not exist. It is possible that in the same way the 

 idea of weight and pressure in raising bodies, or in resisting forces, may 

 in part arise from a consciousness of the amount of nervous energy 

 transmitted from the brain rather than from a sensation in the muscles 

 themselves. The mental conviction of the inability longer to support a 

 weight must also be distinguished from the actual sensation of fatigue 

 in the muscles. 



