62 



SCIENCE. 



[N. S. Vol. XXIII. No. 57G. 



gives, in my opinion, very little informa- 

 tion as to the character of the organic mat- 

 ter, and is only valuable when different 

 surface waters are to be compared with 

 each other, or when used in filtration ex- 

 periments. 



The same may be said as regards color, 

 turbidity and the amount of mineral matter 

 that a surface water contains, that, though 

 of essential importance in deciding on the 

 value of a normal water as a potable water, 

 they give little information as to pollution. 



In the early days of bacteriology it was 

 claimed that the final criterion as to pollu- 

 tion of a water would be furnished by aid 

 of that science, and though this hope has 

 not been fulfilled, the information that can 

 be gained by a bacterial analysis is often 

 of the highest importance. It not only 

 aids in the interpretation of the chemical 

 data, but may of itself show, almost with- 

 out question, that a given water is polluted, 

 for though attempts to isolate special patho- 

 genic germs have generally failed, even in 

 waters known to contain these forms, 

 characteristic sewage forms, like the colon 

 bacillus, can be isolated if they occur in 

 any number in a water. Occurrence of 

 numerous characteristic sewage bacteria 

 can point only to one thing, pollution, and 

 if such forms are found there is no question 

 that the water receives sewage drainage. 

 Bacteriology, however, can not determine, 

 except very roughly, the amount of pollu- 

 tion, or the present condition of the pol- 

 luting matter, nor does it give but very 

 little, if any, information as to past pollu- 

 tion. If the pollution is recent and of 

 any considerable amount, a careful bac- 

 terial examination will show the fact, and 

 probably better and more convincingly 

 than any chemical analysis. If the pollu- 

 tion is more remote, more information can, 

 as a rule, be drawn from chemical than 

 from bacterial data. If the {iolluting 

 matter has filtered through the soil before 



entering the water, bacterial work will not 

 indicate the fact. ^ 



As a general statement, it may be said 

 that a bacterial analysis, while giving in- 

 formation as regards recent and continuous 

 pollution, gives no information as to the 

 past history of a water, and in this respect 

 differs from a sanitary chemical analysis. 



All natural waters contain bacteria, and 

 even if the true colon bacillus does not occur 

 in many normal surface waters, one closely 

 akin to it can often be found if a sufficient 

 amount of the water be taken for examina- . 

 tion. The mere presence of bacteria or 

 even the colon bacillus, if found only in 

 large volumes, does not, therefore, signify 

 pollution. 



The number of bacteria found in a sur- 

 face water depends not only upon the 

 organic matter a water contains, but to a 

 greater or less extent upon various natural 

 causes, such, for instance, as the character 

 of the soil of the watershed, the rainfall, 

 the time of year the examination is made, 

 and these considerations must be taken into 

 account when attempting to determine the 

 character of the water from the number 

 of bacteria present. Arbitrary standards 

 have been proposed from time to time, and 

 of these Dr. Sternberg's, that a water con- 

 taining 500 bacteria to the cubic centi- 

 iiieter is open to suspicion and one con- 

 taining over 1,000 bacteria is presumably 

 contaminated by sewage or surface drain- 

 age, is probably as satisfactory as any that 

 could be devised. Though most artificially 

 filtered waters and many reservoir waters 

 contain not over 100 bacteria to a cubic 

 centimeter, to state that a surface water 

 showing on a single examination a much 

 greater number than 500 per cubic centi- 

 meter was probably polluted, would be 

 unjvistifiable, and the significance of the 

 data can only be determined when the 

 average bacterial count of the water under 

 examination is known, or when it is con- 



