650 



SCIENCE. 



[N. S. Vol. XXI. No. 539. 



man, who stated that all of the physicians 

 in the city were opposed to such a plant, 

 and therefore how could the council, com- 

 posed, as they were, of laymen, run counter 

 to siich weight of professional opinion. 

 The answer was simple and emphatic, 

 namely, that upon such a subject the phy- 

 sicians were no less laymen than were the 

 councilmen themselves, and that the paper 

 prepared by them was of no greater worth 

 than it would have been had it been signed 

 by all the lawyers or all the clergymen of 

 the town. 



Referring to what has been touched upon 

 above, it is a mistake to imderestimate the 

 value of the 'sanitary survey,' by which 

 we mean a thorough knowledge of the 

 source whence a water comes and of the 

 opportunilies for pollution, both constant 

 and occasional, to which it may be exposed. 

 In the writer's judgment it is not too much 

 to say that if but one form of examination 

 be possible, the 'sanitary survey' should 

 be the one selected. 



Then why not rest satisfied with such 

 examination and permanently exclude 

 chemistry and bacteriology from water 

 eases; and why is not the city engineer an 

 authority competent to express final judg- 

 ment upon the matter in hand? 



In reply it may be said that because of 

 the greatly increased public interest in 

 'water supply' which has developed dur- 

 ing recent years, there has arisen a class 

 of men who have devoted nearly their 

 whole time to the consideration of water 

 questions and who have brought to their 

 aid a sufficiency of chemistry, bacteriology 

 and microscopy to satisfy the requirements 

 of their calling. Such men are, because of 

 their special training and experience, en- 

 abled to view the question from more than 

 one side, and their conclusions have, in con- 

 sequence, greater scope. 



Although the writer believes that, taken 

 alone, the 'sanitary survey' is, in the ma- 



jority of cases, the most important form of 

 examination, he begs not to be misunder- 

 stood. 



No amount of inspection could be substi- 

 tuted for the bacterial count in testing the 

 efficiency of a filter plant, nor would it be 

 of value in warding off danger to a ground 

 water arising from the presence of an un- 

 suspected cesspool. 



As showing the utility of the chemical 

 examination, take the following instance 

 for example : 



A well which was most highly prized 

 because of the cool, pleasing taste of its 

 water was found loaded with chlorides and 

 nitrates. Bacteriology gave no indication 

 of pollution, and inspection of the sur- 

 roundings was spurred into energy by the 

 chemical results alone. Sewage, complete- 

 ly oxidized, from neighboring vai;lts was 

 found to account for the abnormal items 

 in the anal.>i;ical results. At the time of 

 the examination no harm was being done, 

 but would the owner of the well be justified 

 in continuing to use such a water and take 

 his chances of the purifying action of the 

 soil being always effective ? 



It is possible that some objection m.ay 

 be raised to the condemning of a water 

 which shows as its only objectionable fea- 

 ture a chemical evidence of 'past pollu- 

 tion. ' If the pollution be truly past and 

 all of the nitrogenous organic matter be 

 represented by nitric nitrogen ; and, fur- 

 ther, if bacterial examination result favor- 

 ably, then wherein lies the objection to the 

 use of a water which, although once pol- 

 luted, has regained its potable qualities? 

 All pure waters, it may be contended, 

 might be classed under such a head ; for, 

 after all, we are bound to use water over 

 again sooner or later, contrive matters how 

 we may. All this is true enough, but there 

 is surely a preference as to the length of 

 time between the date of present use and 

 the period of 'past pollution.' 



