51S THE PHILOSOPHY 



this period ;and,fince the days of David King of the Jews, it 

 has undergone no variation. Befide accidental difeafes, which 

 are more frequent, as well as more dangerous, in the latter 

 periods of life, old men are fubjedled to natural infirmities 

 that originate folely from a decay of the different parts of 

 the body. . The mufcles lofe their tone, the head fhakes, the 

 hands tremble, the limbs totter, the fenfibility of the nerves 

 is blunted, the cavities of the veffels contract, the fecretory 

 organs are obftru(Sled, the blood, the lymph, and the other 

 fluids, extravafate, and produce all thofe fymptoms and dif- 

 eafes which are commonly afcribed to a vitiation of the hu- 

 mours. The natural decay of the folids, 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 or- 

 ganization of the folids. But the efFe^ls refulting from a nox- 

 ious change in the fluids produce the moft alarming fymp- 

 toms. When the fluids flagnate, or if, by a relaxation of the 

 vefleis, an extravafation takes place, they foon corrupt, and 

 corrode the weaker parts of the folids. Hence the caufes 

 of diflblution gradually, but perpetually, multiply, our inter- 

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

 a period to our exiftence. 



With regard to Quadrupeds^ the caufes of their diflblution 

 are precifely the fame with thofe which deflroy the human 

 fpecies. The times of their growth bear, likewife, fome pro- 

 portion to the duration of their lives. But, as we have alrea- 

 dy given a table of the ages at which difi'erent quadrupeds are 

 capable of multiplying their fpecies, and of the general dura- 

 tion of their lives, to avoid unnecelTary repetitions, we muft 

 refer the reader to page !288 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. Moft of them acquire their full 

 dimenfions in a few months, and are capable of multiplying 



