SECTION I 

 THE SPECIAL SENSES 



HOW DIFFERENT EXTERNAL CONDITIONS ACT UPON 

 THE BODY AND HOW WE GAIN KNOWLEDGE OF 

 OUR SURROUNDINGS 



The body has developed both structurally and functionally to 

 enable the individual and the species to survive in the face of external 

 conditions. Hence its capability of modifying its actions to suit 

 its surroundings is of primary importance, and the ways in which 

 external conditions act upon it to bring about appropriate reactions 

 require special study. The body as a machine liberating energy 

 in its activities is acting in subservience to these influences from 

 without. For this reason alone it is reasonable to begin the study 

 of physiology by the investigation of the various receiving arrange- 

 ments by which different kinds of external change produce their 

 definite effects either with or without those modifications of con- 

 sciousness which we call sensations. 



Since it is by changes in our consciousness that we are made aware 

 of our existence, and since these changes are brought about by 

 the stimulation of specially-developed receptors, each of which 

 when stimulated gives rise to a particular kind of sensation, the 

 physiological action of these arrangements may be termed the 

 physiology of the Special Senses. 



A second advantage in taking the Special Senses as the starting 

 point is that, since the methods employed are largely subjective, 

 the use of complicated recording apparatus is not generally necessary. 



A third advantage is that the student early learns the limitations 

 of the senses in gaining knowledge of the outer world, and the 

 danger in interpreting wrongly the sensations experienced. Of all 

 these dangers the greatest to educated people is undoubtedly the 

 element of expectancy with which an observation or experiment is 

 approached. The limitation of our senses must be accepted, but 

 the effects of this element of expectancy can be eliminated, and one 

 of the first things to be learned is to observe honestly and without 

 preconceived ideas. 



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