6l4 PHILOSOPHICAL TRANSACTIONS. [anNO 1722. 



or other die of that distemper ; it follows, that the hazard of dying of it, to 

 the remainder of mankind, above J or 2 years of age, who are all supposed to 

 undergo that disease sooner or later, is that of 72 out of 61 4, or nearly 2 out 

 of 17 : so that no more than between 7 and 8 can recover from that distemper, 

 for 1 that dies of it. And if any considerable part of the aforesaid remainder 

 of mankind, more than is allowed for above, escape having the small-pox, then 

 the proportion of those that recover from it, will be still smaller. 



This consideration shows the fallacy of one plausible argument, that has been 

 often made use of on occasion of the present disputes about inoculation : which 

 is, that whatever be the danger of dying of the small-pox, to those that 

 actually have that disease, yet as great numbers of persons never have the 

 small-pox at all, this danger is what any particular person may never be in ; and 

 therefore it will be madness to undergo the hazard of inoculation, be it great 

 or small, in order to prevent a disease which possibly may never befall one. 



For if 2 parts in 17 of all mankind, that are above 1 or 2 years of age, must 

 sooner or later die of the small-pox, it is plain, that how many parts soever of 

 these 17 are supposed to escape that distemper, the mortality among the re- 

 mainder, who undergo it, must in proportion be so much the greater. As for 

 instance, if 7 parts escape having the small-pox, and 10 undergo it, then 2 out 

 of 10, or I out of 5, that have the small-pox, must die of that disease. 



And as it can never be known, whether any particular person be one of those 

 that are to have the small-pox, his hazard of dying of that distemper, being 

 made up of the hazard of having it, and the hazard of dying of it, if he has 

 it, will be exactly the same, namely, that of 2 in 17, or 1 in 8 or 9, whether 

 the proportion of mankind that escape having the small-pox, be great or 

 small. 



But as what has been said concerning the hazard of the natural small-pox, is 

 taken from an account of 42 years ; whereas the hazard of inoculation is esti- 

 mated only from what has happened in the space of about 1 8 months, since 

 which time it had its first rise among us ; it will perhaps be asked by some per- 

 sons, why we do not likewise make the estimate of the hazard of the natural 

 small pox, from the last 2 years alone, without running back into so great a 

 number of years, before inoculation was begun ? 



To which we answer, that the proportion of those that die of the small- pox, 

 varies so much in different years, as appears from the tables above, that it was 

 impossible to come at any certainty in this point, from the consideration of the 

 last 2 years alone : and if any one suspects us of partiality in proceeding after 

 the manner we have done, he need only cast his eyes on the 2d table, where 

 he will find, that the mortality of the natural small-pox, for the last 2 years. 



