82 SEWAGE AND ITS PURIFICATION 



contain only small quantities of vegetable matter. But the "f 

 difficulties from the smells that they produce have often arisen 

 in lakes and reservoirs in different parts of the w^orld. Odours 

 produced by the living forms have proved to be due in many 

 cases to the secretion of compounds analogous to the essential 

 oils, w^hich have been actually extracted by ether or gasolene ; 

 the oil globules may be seen in many species under the micro- 

 scope, and the effect on the water increases w^hen the organisms 

 divide or disintegrate, especially in the autumn. 



Crenothrix Kithniana or polyspora was first observed in 1852 in 

 the drains from a cultivated field in Silesia, and was described 

 by Kiihn. It is capable of very rapid multiplication and of 

 fouling large quantities of water, which must, however, contain 

 a certain quantity of ferrous iron. Thresh mentions that a few 

 years ago a number of wells in Essex developed smells in the 

 autumn, which he traced to species of Crenothrix ; most of 

 them were free from suspicion of sewage pollution, although 

 the odour was strongly suggestive of sewage. A similar result, 

 with a reddish colour and turbidity, occurred in the reservoirs 

 at Cheltenham in 1896 from a variety of C. polyspora. This or 

 allied species have been connected with an unpleasant odour 

 and appearance in many subsoil waters, but Dr. Garrett has 

 found that the organism has no effect on health. The luxuriant 

 growth of C. Kilhniana at the Berlin waterworks in 1878 ■ 

 proved so troublesome that fresh filter-beds were constructed. 

 It developed to a thickness of some feet in the streams supplying 

 the reservoirs, although the organic matter dissolved in the ■ 

 water was small. Nine years later Rotterdam was similarly 

 affected, and United States records contain numerous examples. 

 In 1891 a strong foetor was communicated to the water-supply 

 of Bolton, Lancashire, by a copious growth of Conferva 

 bomhycina in the reservoirs, and the same occurred in another 

 Lancashire town in 1898. Treatment with minute quantities 

 of copper sulphate has been found to be successful ; I have 

 also noticed that the presence of a very small quantity of 

 available chlorine inhibits many of these growths. 



The following organisms have been specially offensive at 

 various times : 



CyanophycecB. Anahcena^ a bluish-green or brownish fila- 

 mentous alga, family Nostocaceae, accompanied by an odour 

 described as like " horse-dung " in England, " pig-pen " in 

 America. It is remarkable that in A . circinalis, according to 



