304 Of the Consequences Bk. iv. 



to use Dr. Heberden's metaphor, the channels, 

 through which the great stream of mortality is 

 constantly flowing, will always convey off a given 

 quantity. Now if we stop up any of these chan- 

 nels, it is perfectly clear, that the stream of mor- 

 tality must run with greater force through some 

 of the other channels ; that is, if we eradicate 

 some diseases, others will become proportionally 

 more fatal. In this case the only distinguishable 

 cause is the damming up a necessary outlet of 

 mortality.* Nature, in the attainmentof her great 

 purposes, seems always to seize upon the weakest 

 part. If this part be made strong by human skill, 

 she seizes upon the next weakest part, and so on 

 in succession ; not like a capricious deity, with 

 an intention to sport with our sufferings, and con- 

 stantly to defeat our labours ; but, like a kind, 

 though sometimes severe instructor, with the in- 

 tention of teaching us to make all parts strong, 

 and to chase vice and misery from the earth. In 

 avoiding one fault we are too apt to run into some 

 other; but we always find Nature faithful to her 

 great object, at every false step we commit, ready 

 to admonish us of our errors, by the infliction of 

 some physical or moral evil. If the prevalence of 

 the preventive check to population in a sufficient 

 degree were to remove many of those diseases, 

 which now afflict us, yet be accompanied by a 



* The way in which it operates is probably by increasing 

 poverty, in consequence of a supply of labour too rapid for the 

 demand. 



