TRANSACTIONS OF SECTION K. 935 



5. The Sea-weed Ulva latissima and its Relation to the Pollution of Sea- 

 water by Sewage. By Professor Letts, D.Sc, Ph.D., and John 

 Hawthorne, B.A., Qiieen's College, Belfast. 



For a numter of years past a very serious nuisance has arisen from the sloblands 

 of the upper reaches of Belfast Lough during the summer months, the stench at 

 low tide being quite overpowering, and the air heavily charged with sulphuretted 

 hydrogen. A precisely similar nuisance, though not of the same magnitude, also 

 arises from the sloblands in the northern portion of Dublin Bay. 



The nuisance is caused by deposits of the green sea-weed, called Ulva latissima, 

 or sea-lettuce, which in the two localities mentioned grows in abundance, and 

 during high winds or gales is washed ashore. In Belfast Lough the quantity thus 

 deposited is enormous, forming hanks which are often several feet thick, and 

 extend for miles along the coast. Once deposited, these layers of sea-weed often 

 remain more or less stationary for months in the shallow bays or pools of the 

 neighbourhood, and 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 Che7>iical Changes which occur when Ulva latissima ferments in Sea- 

 water. — An extended investigation in the laboratory has shown that when the 

 sea-weed ferments hydrogen and carbonic anhydride are first evolved in about 

 equal proportions by volume, and fatty acids are produced. Isolation and exami- 

 nation of these latter show that propionic acid is the chief; butyric acid is a,l80 

 formed, and probably acetic acid in addition. In a later stage of the fermentation 

 sulphides are formed, probably by reduction of sulphates present in the sea-water, 

 and the sea-weed blackens from formation of ferrous sulphide, and this latter 

 disengages sulphuretted hydrogen by the action of the fatty acids, whence the 

 nuisance. 



Composition of Ulva latissima. — The mean results of the analysis of the dried 

 sea-weed were as follows : — 



Carbon . 

 Hydrogen 

 Nitrogen 

 Oxygen . 

 Ash . 



35-15 

 5-27 

 6-25 



?n^ 4. ■ • r Sulphur 3-21 

 15-37 contammg | j^.^^ 2-20 



10000 



Attempts to isolate any definite principles by the methods of proximate 

 analysis were not very successful, and no carbohydrate beyond cellulose could be 

 identified. 



Bacteriological JExamination. — Considerable difficulty was experienced in 

 attempts to isolate the organisms concerned in the putrefactive processes, and the 

 ordinary methods failed for the greater part. The evidence at present collected 

 points to there being two chief species concerned. (1) A spore-forming bacillus 

 which apparently infests the sea- weed and causes the production of fatty acids from 

 its tissues ; and (2) a second micro-organism, probably derived from the mud^ of 

 the shore, which gives rise to the formation of sulphides by a later fermentative 

 process. 



Ulva latissima in Relation to Setvage Pollution. — The evidence tending to 

 prove that the occurrence of the sea-weed in quantity in any locality is associated 

 with sewage pollution is of three kinds. 



(1) The Composition of its Tissues. — The amount of nitrogen it contains is far 

 in excess of that of any other sea-weed of which analyses are recorded. It contains 

 over 6 per cent., and resembles in nitrogen content an animal product rather 

 than a vegetable. (Dry cheese contains about 7, and dry milk about 5 per cent., 

 whereas peas only contain about 4 and meadow hay 2 per cent.) 



