340 COORDINATION AND SENSATION 



known as the special sensations. The others, including 

 the sensations of pain, hunger, thirst, nausea, fatigue, 

 comfort, discomfort, and those of disease, are known as 

 organic, or general, sensations. These two classes of sen- 

 sations differ in their purpose in the body as well as in the 

 manner of their origin. 



Purposes of Sensations. '.Any given sensation is related 

 to the stimulus which excites it as an effect to a cause. It 

 starts up or stops, increases in intensity or diminishes, 

 according to the action of the exciting stimulus. As the 

 stimuli are outside of the nervous system, and in the 

 majority of cases outside of the body, the sensations in- 

 dicate to the mind what is taking place either in the body 

 itself or in its surroundings. They supply, in other words, 

 the means through which the mind acquires information. 

 By means of the special sensations, a knowledge of the 

 physical surroundings of the body is gained, and through 

 the organic sensations the needs of the body and the state of 

 the various organs are indicated. In general, sensations are 

 made to serve two great purposes in the body, as follows : 



1. They provide the necessary conditions for intelligent 

 and purposeful action on the part of the body. 



2. They supply the basis for the higher mental activi- 

 ties, as perception, memory, thought, imagination, and 

 emotion. 



Intelligent action is impossible without a knowledge 

 both of the bodily organs and of the body's surroundings. 

 Protection and the regulation of the work of an organ 

 necessitate a knowledge of its condition, while the adapt- 

 ing and adjusting of the body to its surroundings require 

 a knowledge of what those surroundings are. The 

 dependence of all the higher forms of mental activity upon 

 sensations is recognized by psychologists and is easily 



