NATURAL THEOLOGY. 125 



from any of our senses depend upon an original 

 congruity between the sense and the properties 

 perceived by it, we know by experience that the 

 adjustment demanded, with respect to the quali- 

 ties which we conferred upon the objects that sur- 

 round us, not only choice and selection, out of a 

 boundless variety of possible qualities with which 

 these objects might have been endued, but di pro- 

 portioning also of degree, because an excess or de- 

 fect of intensity spoils the perception, as much al- 

 most as an error in the kind and nature of the 

 quality. Likewise the degree of dulness or acute- 

 uess in the sense itself is no arbitrary thing, but, 

 in order to preserve the congruity here spoken of, 

 requires to be in an exact or near correspondency 

 with the strength of the impression. The dulness 

 of the senses forms the complaint of old age. 

 Persons in fevers, and, I believe, in most maniacal 

 cases, experience great torment from their preter- 

 natural acuteness. An increased, no less than an 

 impaired sensibility, induces a state of disease and 

 suffering. 



The doctrine of a specific congruity between 

 animal senses and their objects is strongly favour- 

 ed by what is observed of insects in the election of 

 their food. Some of these will feed upon one kind 

 of plant or animal, and upon no other ; some ca- 

 terpillars upon the cabbage alone ; some upon the 

 black currant alone. The species of caterpillar 

 which eats the vine will starve upon the alder ; 

 nor will that which we find upon fennel touch the 

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