234 Proceedings 0/ the Boyal 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, &c., 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 Mark's Place, consisted of those organic growths passing 
into an active state of putrescence. During 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 w^ater, 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 putrefaction 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 Naidina, and are named Tuhifex 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 
