OF NATURAL HISTORY. 511 



toms and difeafes which are commonly afcribed to a vitiation of the 

 humours. The natural decay of the foUds, however, appears to be 

 the original caufe of all thefe maladies. It is true, that a bad ftate 

 of the fluids proceeds from a depravity in the organization of the 

 folids. But the effeds refulting from a noxious change in the fluids 

 produce the mofl: alarming fymptoms. When the fluids ftagnate, or 

 if, by a relaxation of the veflels, an extravafation takes place, they 

 foon corrupt, and corrode the weaker parts of the folids. Hence the 

 caufes of difTolutlon gradually, but perpetually, multiply, our inter- 

 nal enemies grow more and more powerful, and at laft put a period 

 to our exlftence. 



With regard to ^adrupeds, the caufes of their dilTolutlon are pre- 

 cifely the fame with thofe which deftroy the human fpecies. The 

 times of their growth bear, likewife, fome proportion to the dura- 

 tion of their lives. But, as we have already given a Table of the 

 ages at which different quadrupeds are capable of multiplying their 

 fpecies, and of the general duration of their lives, to avoid unnecef- 

 fary repetitions, we muft refer the reader to page 283. of this work. 



Some Birds afford inftances of great longevity. In this clafs of 

 animals, the duration of life is by no means proportioned to the 

 times of their growth. Mod of them acquire their full dimenfions 

 in a few months, and are capable of multiplying the fpecies the firft 

 fpring or fummer after they are hatched. In proportion to the fize 

 of their bodies, birds are much more vivacious, and live longer than 

 either men or quadrupeds. Swans have been faid to live three hun- 

 dred years ; but, though mentioned by refpeftable writers, the af- 

 fertion is not fupported by any authentic evidence. Mr Willough- 

 by, in his Ornithology *, remarks, ' We have been aflured by a 



' friend 



• Page 14. 



