1054 



SENSES 



the muscular sense. The muscle-spindles or neuro-muscular spindles 

 (Fig. 448), peculiar structures which occur in large number in most 

 of the skeletal muscles, and have been carefully studied by Huber, 

 Sihier, Ruffini, and other observers, are the terminations of many of 

 the sensory fibres. They are long narrow bodies, with a thick sheath 

 of connective tissue enclosing fine striped muscular fibres. Medul- 

 lated nerve-fibres enter the spindle, and there, dividing into branches 

 and losing their medullary sheath, form endings of various kinds aroun4 

 and between the muscular fibres. It is possible that in contraction 

 of the muscles the nerve-fibres in the spindles are compressed, and thus 

 nechanically stimulated. 



In the spinal cord these impulses are conducted up through the 

 posterior column; and, although less is known as to the paths they 

 follow in the higher parts of the central nervous system, it is certain 

 that there is some afferent bond of connection between the cortical 

 motor areas and the muscles which they control (p. 929). 



Tactile sensations set up in the skin or mucous membrane lying 

 over contracting muscles may also help the nervous motor mechanism 

 in appreciating and regulating the amount of contraction ; but the fact 

 that, in anaesthesia of the mucous membrane covering the vocal cords 

 produced by cocaine, the voice is not at all impaired, shows that mus- 

 cular contractions of extreme nicety can be carmed on without any 

 such aid. 



Sensations of Hunger and Thirst. These are representatives of 

 the group of interior sensations. As Tiedemann pointed out long 

 ago, at least two elements are involved in the somewhat vague 

 sensation of hunger: the local sensation of emptiness in the stomach, 

 and the general sensations of malaise, depression, and weakness. 

 There is some evidence that the general sensations are in part at, 

 least dependent upon the state of the stomach. But it would 

 appear thatat any rate, during prolonged deprivation of food a 

 general condition of the tissues may exist which can arouse in con- 

 sciousness the sensation of hunger, even after the stomach has been 

 amply filled. Thus a patient with a fistula in the upper part of 

 the small intestine constantly suffered from hunger in spite of the 

 enormous quantities of food consumed. The stomach always felt 

 full, but as most of the food escaped from the fistula, the tissues 

 continued to be starved, and the general sensation of hunger re- 

 mained (Hertz). In diabetes the same thing may be observed. 

 On the other hand, it was noted by Carlson and one of his pupils 

 that after a fast of five days practically all of the mental depression 

 and some of the feeling of weakness disappeared during the first 

 meal. He therefore concluded that the depression of the central 

 nervous system was essentially a reflex condition, depending prob- 

 ably on afferent impulses from the digestive tract, rather than a 

 result of deficiency of nutrient material in the blood. Complete 

 recovery from the bodily weakness, however, did not take place 

 till the second or third day after breaking the fast. 



An important factor in the local sensations associated with 

 hunger is the strong periodical contractions of the empty stomach, 



