LETTERS TO BROTHER JOHN. 1)9 



Every organ, therefore, has a peculiar SENSI- 

 BILITY of its own, and can be properly affected by 

 certain stimuli only all others, if they affect it at 

 all, affecting it injuriously : and the evidence of the 

 impropriety of a stimulus, is the pain, or some other 

 inconvenience produced. Hence arises a corollary; 

 viz. that whatever stimulus produces pain, or other 

 inconvenience, is an improper stimulus. The pain, 

 for instance, produced by blowing salt into the eye 

 is sufficient proof that salt is a stimulus not proper 

 to that organ, and cannot, therefore, be applied to 

 it without injury. 



This peculiar, distinctive, or eclectic or natu- 

 ral SENSIBILITY, is impaired by over-stimulation. 

 Thus we may be deafened by excess of sound, and 

 blinded by excess of light. Every body knows, too, 

 that snuff will produce, in persons not accustomed 

 to it, violent and painful sneezing ; while those who 

 have been industriously stimulating their nostrils 

 with it for some time can take the strongest kinds 

 with impunity. Again, persons who have never 

 smoked tobacco will generally be sick when they 

 first begin to do so ; but after a short time they can 

 smoke pipe after pipe without inconvenience. If a 

 person not accustomed to drink any thing stronger 



than water were to swallow a glass of whisky, it 

 F 2 



