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. 



