BACTERIA OCCURRING IN SEWAGE 83 



Jackson and Ellms,^ the dry substance contains 9*66 per cent, 

 of nitrogen, a higher percentage than that found by Letts in 

 JJlva latissima (6' 18 per cent.), and much higher than is 

 recorded for others of the larger algse (1*3 to 4*6). The " pig- 

 pen " odour is attributed to " the breaking down of highly 

 organized compounds of sulphur and phosphorus, and to the 

 presence of the high percentage of nitrogen." Analysis of the 

 Igas evolved during decomposition gave in volumes per cent. : 

 hydrogen 82*4, CH4 0*8, N 12*4, CO2 1*5, O 2*9 ; the oxygen 

 ,and a portion of the nitrogen probably represented residual air, 

 tand a large quantity of the CO2 produced remained dissolved 

 ;in the water surrounding the plant. Oscillaria^ Nostoc, and 

 Lyngbya (the latter with " a peculiar suffocating odour ") 

 belong to the same family, and have a similar effect. I have 

 found the two former and Anabaena in some English water- 

 supplies, notably in June, 1905, in a portion of a Surrey supply 

 of high organic and bacterial purity. Lyngbya was present in 

 the Cheltenham reservoir. CcelosphcBvium is mentioned in the 

 Brooklyn Board of Health reports as having caused smells, 

 and as being one of the worst of its class. Many of the Chloro- 

 phycecB, or green microscopic algae, impart strong fishy or sea- 

 weed odours. Volvox, formerly classed among the protozoa, is 

 conspicuous in its fishy smell ; I found this organism in the 

 harbour water at Chichester, and there are records of its effect 

 on English public water-supplies. 



" Aromatic " is the general term applied to the volatile pro- 

 ducts of the DiatomacecB, and in foreshore muds I have noticed 

 that a peculiar aromatic smell was associated with large 

 numbers of these organisms. But many of them are much 

 more unpleasant, and I discovered several of the odorous forms 

 'at Chichester in 1901 (see Chap. XIII.). Asterionella causes a 

 disagreeable fishy smell. Like other green organisms, it grows 

 most luxuriantly in ground water exposed to the light. In the 

 States it has occasioned great inconvenience ; in 1896 the 

 reservoir supplying Brooklyn contained 25,000 to 30,000 per ex. 

 I have found it in a few English drinking-waters, as also 

 Synedra, which is credited with a disagreeable " grassy" smell. 

 Whipple records an instance of a large mass of water being 

 rendered offensive by the breaking up by a storm of a thick 

 marginal growth of Melosira varians. 



^ " Odours and Tastes of Surface Waters," United States Technology Quarterly^ 

 X., December, 1897. 



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