GENERAL SENSATIONS. 267 



the sense of taste by acting on the ends of nerves in the 

 mouth. Different nerve endings then, are adapted to re- 

 ceiving impressions from the action of different forces. 



Nerve endings in different parts of the body may be affected 

 by the blood and the lymph, and give us sensations of comfort 

 or discomfort, restlessness, fatigue, faintness, etc. These are 

 called General Sensations. They are probably due to the con- 

 dition of the blood, or to the condition of nutrition of the 

 .various parts of the body. Thus after muscular exercise the 

 muscles are acid in their reaction, while they are alkaline after 

 resting ; after exercise carbon dioxid accumulates in them to 

 a certain extent. Hunger and thirst come on after abstinence 

 from food and drink, or after work exhausting the tissues. 

 The presence of the various waste products, or the condition 

 of the cells as the result of their activity, acting through the 

 nerve endings, in the tissues, keep the nerve centers informed 

 as to the condition of the parts of the body. If these condi- 

 tions are extreme we may have definable sensations ; but ordi- 

 narily the sensations are of an undefinable sort, which we 

 designate as " general sensations." 



In experiment electricity is usually the best stimulus ; 

 mechanical stimuli, as "ufed in the experiments with the 

 muscle-nerve preparation from the frog, by cutting or pinch- 

 ing the nerve, may be employed ; hea"t, as in touching the 

 nerve with a hot wire, or holding a hot wire near the nerve, 

 may be used as a stimulus ; chemical stimuli, as acids, strong 

 salt solution, etc., may also be used. 



It is to be noted that while special stimuli act on specially 

 modified nerve endings, all nerve fibers are essentially alike ; 

 and the nerve impulse, however started, is probably the same 

 kind of force. For instance, cutting the optic nerve, or severe 

 shock, as a blow on the head, causes a sensation of light not 

 quite so definite, but essentially the same as though light had 



