1900-1901.] Prof. Letts and Mr Hawthorne on Ulva latissima . 269 
In the upper reaches of Belfast Lough this weed grows in 
abundance, and during high winds or gales it is washed ashore, 
often in enormous quantities, forming hanks which are frequently 
two or three feet thick, and extend at times for miles along the 
coast, especially on the southern shore. 
Once deposited, these layers of weed often remain more or less 
stationary in the shallow hays or pools of the neighbourhood for 
months, and under these circumstances, and particularly in warm 
weather, rapid putrefaction occurs, and a perfectly intolerable 
stench arises, which is perceptible over a wide area, and seriously 
affects, not only the comfort of the inhabitants of the district, but 
the value of their property also. 
The investigation, the results of which we describe in the 
following pages, was originally undertaken with the view merely 
of ascertaining the cause of the nuisance arising from the slob- 
lands of Belfast. But we were gradually led into a more extended 
inquiry, which has embraced not only a study of the chemical 
changes which occur when Ulva latissima ferments, but in addition,, 
an examination of the composition and characters of the weed 
itself, the isolation of the products of its fermentation, and attempts 
to isolate the particular organisms giving rise to these products 
and finally we have endeavoured to ascertain, both experimentally 
and by an examination of localities in which the weed is either 
present in quantity or is virtually absent, the relationship of Ulva, 
latissima to the pollution of sea water by sewage. 
Por the sake of clearness and convenience we shall give the 
results of our inquiry into these different questions in a somewhat 
different order from that in which they were obtained. 
The Chemical Changes which occur when Ulva latissima ferments. 
A quantity of the fresh weed was carefully washed in several 
changes of ordinary tap water until free from shells and debris of 
various kinds,* and it was then distributed between two flasks, 
one of which was filled with tap water and the other with sea 
* The weed, as obtained by us from the Belfast foreshore, was nearly always 
infested with minute spiral shell-fish, which feed upon it and eat out circular 
holes. 
