62 Origin, or Process of Causation of the Series. [CHAP. in. 



them happen to be missing. Thus we know that the length 

 of life is on the whole tolerably regular, and so are the 

 numbers of those who die in successive years or centuries 

 of most of the commoner diseases. But it does not seem 

 to be the case with all diseases. What, for instance, of 

 the Sweating Sickness, the Black Death, the Asiatic 

 Cholera ? The two former either do not recur, or, if they 

 do, recur in such a mild form as not to deserve the same 

 name. What in fact of any of the diseases which are 

 epidemic rather than endemic ? All these have their causes 

 doubtless, and would be produced again by the recurrence 

 of the conditions which caused them before. But some of 

 them apparently do not recur at all. They seem to have 

 depended upon such rare conditions that their occurrence 

 was almost unique. And of those which do recur the course 

 is frequently so eccentric and irregular, often so much de 

 pendent upon human will or want of will, as to entirely 

 deprive their results (that is, the annual number of deaths 

 which they cause) of the statistical uniformity of which we 

 are speaking. 



The explanation probably is that one of the principal 

 causes in such cases is what we commonly call contagion. 

 If so, we have at once a cause which so far from being fixed is 

 subject to the utmost variability. Stringent caution may 

 destroy it, carelessness may aggravate it to any extent. The 

 will of man, as finding its expression either on the part of 

 government, of doctors, or of the public, may make of it 

 pretty nearly what is wished, though against the possibility 

 of its entrance into any community no precautions can ab 

 solutely insure us. 



9. If it be replied that this want of statistical regu 

 larity only arises from the fact of our having confined our 

 selves to too limited a time, and that we should find 



