234: Proceedings of the Royal Physical Society. 



The chemical analyses of these organic growths demon- 

 strated, that even when examined with all the adhering 

 entangled filth, when dried, they contained, on the average 

 of seven samples. 50-61 per cent, of organic matter, of which 

 0'84 consisted of nitrogen. These organic matters are being 

 constantly detached from the stones, Sec, on which they grow, 

 and the torn-off fragments float down the stream or lade and 

 form part of some deposit in a rocky pool or in the still water 

 above a dam or call. A considerable proportion of the 

 deposits observed in the bed of the Water of Leith behind 

 Ainslie Place and [Moray Place, and in the large cesspool at 

 St Clark's Place, consisted of those organic growths passing 

 into an active state of putrescence. Daring the spring 

 months the growths are apparently stronger, and form 

 longer streamers than during the summer months. The 

 temperature of the latter is higher, and facilitates changes 

 such as the disintegration of the mass. These growths 

 appear to be the last stage of organic life which will inhabit 

 foul water, but in places where in the spring many patches 

 of the growth were observed, in summer hardly any was to 

 be noticed. This disappearance, in part at least, of the 

 growth is attributed to the more foul state of the sewers 

 and Water of Leith in summer, which leads in some places 

 to such a rapid putref action as even to arrest the develop- 

 ment of this comparatively simple form of organic life. 



In the whole course of the "Water of Leith from Coltbridge 

 downwards not a single fish could be seen. The animal life 

 which was specially visible to the naked eye consisted of 

 colonies of small red worms, which were very abundant in 

 many places, and are regarded as the last remnant of animal 

 life which will exist in water contaminated by sewage. 

 These minute red worms are a kind of Nais, belonging to 

 the family of Xaidina. and are named Tubifex rivulorum. 

 They are found in greater abundance in the Water of Leith 

 during spring than in summer, apparently from the more 

 active putrescence of the sedimentary matter leading in the 

 summer to the disengagement of a more full supply of 

 noxious gases, which even these minute worms cannot sur- 

 vive. In many places, where in spring the bed of the 



