8o SEWAGE AND ITS PURIFICATION 



Boyce, indicates much greater pollution (he states that it is 

 favoured by warmth and the presence of H2S, but requires 

 oxygen for its development, therefore will not grow in crude 

 sewage, but may cause blocking of aerobic contact beds). 

 Carchesium lachmanni, a protozoon allied to Vorticella, found in 

 great masses under similar conditions to those of the Sphaero- 

 tilus. The occurrence of these organisms is described by 

 Boyce in the Second Report of the Royal Commission on 

 Sewage, 1902, p. 104, by whose kind permission I reproduce 

 the figures in Plates V. and VI. 



Organisms causing Odours. 



I have found in some cases that foreshore odours have been 

 attributed to the entrance of effluents when they ^ have been 

 really caused by ordinary marine and fluviatile life. Thus in a 

 harbour scum which I recently examined the odour was very 

 powerful, being described as strongly earthy, weedy, and some- 

 what fishy, and was undoubtedly due to the organisms. 

 Among those specially mentioned as causing unpleasant odours 

 which were identified were the diatoms Melosira, Tabellaria, 

 Diatoma, Meridion, with Volvox, Oscillaria, Ulothrix, Beg- 

 giatoa, and Spongilla. Similar occurrences were described by 

 Sir E. Frankland in his report on the alleged pollution of Loch 

 Long and Loch Goil in 1889, and he was of opinion they were 

 not due to contamination by sewage. 



A green frondose seaweed, Ulva lactiica or latissinia, " sea- 

 lettuce," widely distributed on the coast, is sometimes washed 

 ashore, and forms banks of a strongly fishy odour, which in 

 decaying emit a putrid gas. As this evil is acute in Belfast 

 Lough, Professor Letts has subjected the plant to examination.^ 

 The mean results of analysis of the dried substance were, in 

 per cents : C, 35*15 ; H, 5*27 ; N, 6*25 ; O, 37-96 ; ash, 15*37, 

 containing S, 3*21, and Fe, 2*20 ; and the proximate analysis 

 showed in per cents : Chlorophyll, fats, etc., 17 ; albuminoids 

 or proteids, 33 ; cellulose, 50. No carbohydrate beyond cellu- 

 lose was identified. In fermentation the weed at first evolves 

 about equal volumes of CO2 and H, while fatty acids are 

 produced, chiefly propionic, with butyric and probably acetic. 



1 " Absorption of Ammonia from Water by Algce," Report of British Associa- 

 tion, 1900, p. 935 ; " Ulva latissima and its Relation to the Pollution of Sea- water 

 by Sewage," Letts and Hawthorne, Procd5r?/7/^5 of the Royal Society of Edinburgh, 

 March 4, 1901 ; Report of Commission on Sewage, vol ii., 1902, p. 469 ; Second 

 Report on the Scheme of Sewage Purification for Belfast, by Dr. Letts, 1904. 



