OF WATER FOR ORGANIC MATTER. 43 



people to suppose that every drop of water was inhabited ; 

 that nevertheless water, generally considered very pure 

 for drinking, might contain some forms not possessed with 

 distinct locomotion ; that whenever distinct locomotion 

 began, especially among soft-bodied forms, the water was 

 more than suspicious; that forms increased with the 

 quantity of organic matter containing nitrogen, until the 

 amount was so great as to cause gases of decomposition 

 which eventually stifled life. 



If the water was impregnated with sewage-water (as the 

 Thames at London for example), bad cases excepted, the 

 amount of vegetation which spread over the sides of a 

 bottle filled with it and set in the sun, was so great as to 

 give the appearance of one solid mass. If the water were 

 taken from the river above Reading, the amount of vege- 

 table matter was seen as a delicate green colouring of the 

 bottom of the vessel ; and if it were taken up at the source, 

 no greenness whatever appeared, but, after long standing, 

 minute crystals of limestone. If the water contained 

 sewage, the phosphates and magnesia were generally found 

 collected in some form of the Navicula, frequently in large 

 masses of the Navicula fulva, and with it also was found 

 phosphoric acid and magnesia. It was sufficient to note 

 the condition of the water with relation to these de- 

 posits to ascertain at what part of the Thames the specimen 

 was taken ; and without the examination of these deposits, 

 I do not consider that it would have been possible to obtain 

 a distinct idea of the nature of the organic matter present. 

 It is, however, needful that we know the general character 

 of the water ; had we a specimen from another situation 

 and found no deposit whatever, it would have been very 

 unfair or very unwise to conclude that it was similar in 

 quality to that from the source of the Thames. It might 

 have been saturated with nitrates, and even a large 

 amount of organic matter not capable of taking the forms 



