64 NATURAL THEOLOGY. 



of our bodies. There may possibly also be some 

 few examples of the second class, in which not 

 only the operation is unknown, but in which ex- 

 periments may seem to prove that the part is not 

 necessary ; or may leave a doubt how far it is 

 even useful to the plant or animal in which it is 

 found. This is said to be the case with the spleen, 

 which has been extracted from dogs without any 

 sensible injury to their vital functions. Instances 

 of the former kind, namely, in which we cannot 

 explain the operation, may be numerous ; for they 

 will be so in proportion to our ignorance. They 

 will be more or fewer to different persons, and in 

 different stages of science. Every improvement 

 of knowledge diminishes their number. There is 

 hardly, perhaps, a year passes that does not, in the 

 works of nature, bring some operation, or some 

 mode of operation, to light, which was before un- 

 discovered, — probably unsuspected. Instances 

 of the second kind, namely, where the part ap- 

 pears to be totally useless, I believe to be ex- 

 tremely rare ; compared with the number of those 

 of which the use is evident, they are beneath any 

 assignable proportion, and perhaps have been 

 never submitted to a trial and examination suffi- 

 ciently accurate, long enough continued, or often 

 enough repeated. No accounts which I have seen 

 are satisfactory. The mutilated animal may live 

 and grow fat (as was the case of the dog deprived 

 of its spleen,) yet may be defective in some other 

 of its functions, which, whether they can all, or in 



