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SCIENCE 



[N. S. Vol. XXIX. No. 747 



little observation of the habits of horses to 

 establish its fallacy. Would you, as intel- 

 ligent people, who have watched horses 

 upon occasion, care to pin your faith upon 

 the "horse-test" as indicating the purity 

 of your household drinking water? 



When I was a boy the belief existed that 

 the presence of many flies tended towards 

 a healthful summer, because they were held 

 to be the means of removal of much waste 

 material which would otherwise decay and 

 taint the atmosphere. We now know that 

 flies are a source of danger in that they do 

 not wipe their feet before crawling over 

 our food. In this connection note the dis- 

 astrous typhoid fever outbreaks in our 

 military camps during the Spanish war. 

 Those epidemics were occasioned by the in- 

 oculation of food by flies; flies that visited 

 the latrines first and the kitchens after- 

 wards. 



Returning now to the water question, the 

 time-honored dictum that a clear, bright 

 water is of necessity a wholesome one is 

 also still widely trusted ; but it reminds me 

 of the ruling of a Mississippi chancellor in 

 a case with which I was once connected. 

 His honor threw all the expert testimony 

 out of court with the remark that the ordi- 

 nary citizen is able well enough to tell 

 whether or not a given water is fit to drink. 

 To illustrate how far the court fell short of 

 the truth in this instance, let me say that 

 not long ago the clear and bright effluent 

 from the Saratoga sewage septic tank was 

 placed in a show window in western New 

 York alongside of an exhibit of the local 

 water supply, to the apparent disadvantage 

 of the latter. Poor as the town water was, 

 it could scarcely have been fair to compare 

 it with filtered sewage and yet his honor 

 from Mississippi would have judged other- 

 wise. 



The "test of experience" is constantly 

 appealed to in support of the alleged 

 purity of some favorite water, and the plea 



that "my family has used the supply for 

 half a century" is considered an argument 

 beyond danger of refutation, it being over- 

 looked that a family, or even several fam- 

 ilies, can not furnish a sufficient number 

 of persons to make the "experience test" 

 valuable; for, be it remembered, a water 

 known to be dangerously polluted will not 

 transmit disease to all, nor nearly all, of 

 those who drink it. As a matter of fact, 

 when one considers the question from a 

 numerical standpoint, basing his investiga- 

 tion upon the population of a large com- 

 munity, the conclusion is forced upon him 

 that the per capita danger from polluted 

 water is really small. Thus, in a city of 

 100,000 inhabitants, which I have in mind, 

 the high typhoid death rate, manifestly 

 caused by bad water, was about 90 per 

 year; which means that over 99,000 of the 

 people did not have the disease at all. 



Now how about this great majority of 

 the citizens that escaped. They would not 

 be likely to testify as to the dangers of the 

 water supply. As you see, the risk is small 

 and it takes a large community to make 

 data about it valuable, but relatively small 

 though it be, it nevertheless is a good in- 

 vestment for a city to avoid it, because 

 hiunan life has a money value and the town 

 which cuts its typhoid rate in half by the 

 erection of a filter plant receives very quick 

 return for the funds expended. 



Doubtless one reason why so many 

 people deny the existence of danger lurk- 

 ing in some specific drinking water is be- 

 cause of the non-dramatic character of the 

 attack. 



Let us suppose that a city has a yearly 

 typhoid death rate of 75, which means that 

 750 people per 100,000 inhabitants have 

 the disease each year and that 75 of them 

 die. The impression upon the community 

 is not really felt except by those whose 

 homes are invaded and the remainder of 

 the population would be likely to resort to 



