690 TEXT-BOOK OF PHYSIOLOGY 



and in breadth from 0.15 to 0.4 mm. Each spindle (Fig. 281) consists of a 

 connective-tissue capsule containing from two to ten longitudinally arranged 

 striated muscle-fibers of fine diameter. In the middle or equatorial region of 

 these intra-fusal fibers there is frequently found a quantity of non-striated 

 protoplasmic matter. The spindle is supplied with both sensor and motor 

 nerves. The sensor fiber loses its external investments as it approaches the 

 capsule. The naked axis-cylinder then penetrates the capsule, and after 

 dividing several times terminates in a ribbon-like or spiral manner around the 

 intra-fusal muscle-fiber. This ending was described by and is known as 

 Rufimi's " annulo-spiral ribbon." The motor nerve also penetrates the 

 capsule and terminates in the polar extremities of the intra-fusal fiber. 

 Sensor end-organs supposed to be connected with the muscle sense are also 

 found in the tendons of muscles. 



Afferent Nerves. That muscles are abundantly supplied with afferent 

 nerves has been proved by different methods of investigation. With histo- 

 logic methods Sherrington has traced afferent fibers from the muscle spindles 

 directly into the spinal nerve ganglia. The contractions of muscles from 

 electric stimulation as well as the contractions known as muscle cramp, 

 due to unknown agents, give rise to sensations of pain, a fact which in- 

 dicates the presence in muscles of afferent or sensor nerves. 



Cortical Area. Pathologic findings have shown that an impairment 

 or a loss of the muscle sense is associated with destructive lesions* of perhaps 

 the super- and sub-parietal convolutions (Figs. 247 and 248). In a case re- 

 ported by Starr the removal of a small tumor in the pia mater situated 

 over the junction of the superior and inferior parietal lobules was followed 

 by a loss of the muscle sense and marked ataxia in the right hand for a 

 period of six weeks, after which recovery took place. These symptoms 

 were attributed to injury of the cortex from unavoidable surgical procedures. 



The muscle sensations, as stated in foregoing paragraphs, form the 

 basis of the perception not only of the direction and the duration of a body 

 movement and the resistance experienced, but also of the position and the 

 tension of the muscle groups. The latter fact more especially makes it 

 possible for the mind to direct the muscles and to graduate the energy 

 necessary to the accomplishment of a definite purpose. 



Active Touch. Active touch or the application of the fingers to the 

 surfaces of external objects implies the cooperation of the skin and the 

 muscles. The sensations which are evoked are combinations of contact 

 and muscle sensations. The union of these sensations forms the basis of 

 the perception of hardness, softness, smoothness, and roughness of bodies. 



THE SENSE OF TASTE 



The sense of taste may be defined as the sense by which the specific 

 quality or flavor of a substance, applied to the taste organ is perceived. 

 This sense is located mainly in the mucous membrane covering the surface 

 of the tongue. 



The physiologic mechanism involved in the sense of taste includes the 

 tongue, the gustatory nerves, their cortical connections and nerve-cells in the 

 gray matter of the sub-collateral convolution. The peripheral excitation of 

 this apparatus gives rise to nerve impulses which transmitted to the brain 



