236 Proceedings of the Royal Physical Society, 
and in shallow parts of the Water of Leith, as at St Mark's 
Place, and which was said to neutralise in great part the 
deleterious effects of the gaseous exhalations, and even to lead 
to the disengagement of oxygen gas in large volumes. A con- 
siderable quantity of the green slime was separated as well 
as practicable from the underlying filthy sediment, and 
having been placed in a bottle till it was filled, the bottle 
was then inverted in a basin, and immediately gases began 
to be evolved. On testing these gases in about three hours, 
there were found carbonic acid 1340 per cent., oxygen 1-60 
per cent., and other gases, which were combustible with a 
bluish-white flame, 85 per cent. It was proved, therefore, 
that this green slime does not practically lead to the dis- 
engagement of oxygen, and indeed the gases which are 
evolved therefrom are essentially identical with those ob- 
tained from any foul deposit in a sewer or in water con- 
veying sewage. 
Moreover, the green slime, when collected from the sur- 
face of the sedimentary matter, and placed in a bottle which 
it filled about one-third, and the remaining two-thirds being 
left as common air, it was found that in forty hours the 
composition of the atmosphere had so materially changed, 
that a lighted taper was immediately extinguished on being 
introduced. A chemical analysis proved that the atmosphere 
left in the bottle contained 11-56 per cent, of carbonic acid, 
only 2*01 per cent, of oxygen, and 8643 per cent, of other 
gases, which in their mixed state were not combustible, and 
did not support combustion. These two experiments, there- 
fore, demonstrated that practically the evolution of oxygen 
gas from the green slime covering a mass of putrescent filth 
was at a minimum, and was highly problematical, whilst the 
disengagement from the mass of carbonic acid and of com- 
bustible gases was undoubtedly certain. The green slime, 
on being examined microscopically, was found to consist 
mainly of minute organisms belonging to the Phytozoa, and 
which are alternately regarded as animals and plants. At 
present, the Euglena viridis, which forms a part at least of 
the green matter of these deposits, is considered to be a plant 
by some naturalists, and an animal by other authorities. 
