2GG d'aleivibert. 



cliauc3 of escaping entirely from an attack of small-pox during 

 his life, or at least of recovering if attacked. 



D'Alembert thinks that the prosj^ect held out to an individual 

 of a gain of three or four years in the probable duration of his 

 hfe, may perhaps not be considered by him to balance the im- 

 mediate danger of submitting to Inoculation. The relative value 

 of the alternatives at least may be too indefinite to be estimated ; 

 so that a person may hesitate, even if he does not altogether 

 reject Inoculation. 



482. D'Alembert lays great stress on the consideration that 

 the additional years of life to be gained form a remote and not 

 a present benefit ; and moreover, on account of the infirmities of 

 age, the later years of a life must be considered of far less value 

 than the years of early manhood. 



D'Alembert distinguishes between the physical life and the 

 real life of an individual. By the former, he means life in the 

 ordinary sense, estimated by total duration in years ; by the latter, 

 he means that portion of existence during which the individual is 

 free from suffering, so that he may be said to enjoy life. 



Again, with respect to utility to his country, D'Alembert dis- 

 tinguishes between the p)liysical life and the civil life. During 

 infancy and old age an individual is of no use to the state ; he 

 is a burden to it, for he must be supported and attended by 

 others. During this period D'Alembert considers that the indi- 

 vidual is a charge to the state ; his value is negative, and becomes 

 positive for the intermediate periods of his existence. The civil 

 life then is measured by the excess of the productive period of 

 existence over that which is burdensome. 



Relying on considerations such as these, D'Alembert does not 

 admit the great advantage which the advocates for Inoculation found 

 in the fact of the prolongation of the mean duration of human 

 life effected by the operation. He looks on the problem as far 

 more difficult than those who had discussed it appeared to have 

 supposed. 



483. We have seen that Daniel Bernoulli assumed that the 

 small-pox attacked every year 1 in ii of those not previously 



