1900 - 1901 .] Prof. Letts and Mr Hawthorne on Ulva latissima. 277 
Although these results are not entirely satisfactory or con- 
cordant, they certainly point to the occurrence of acetic as well as 
propionic and butyric acids among the products of the fermenta- 
tion of ulva in sea water, but the identification of the former 
with certainty was not possible, owing to the smallness of the low 
boiling fraction and the difficulties attending the separation of a 
given acid of the fatty series from a mixture with its homologues. 
But the boiling point and higher specific gravity of the low 
boiling fraction, as well as the percentage of barium found in the 
barium salt obtained from it, can scarcely be accounted for except 
on the assumption that it contained acetic acid. 
Our experiments on the fermentation of Ulva latissima in sea 
water thus afford evidence that at least three members of the fatty 
series of acids are produced : of these, however, propionic acidity 
formed in by far the largest quantity. 
The Composition of the Tissues of Ulva latissima. 
The occurrence of the ulva in two localities (Dublin harbour 
and Belfast Lough) in considerable quantities where crude sewage 
makes its way into the sea, and the experiments just recorded on 
the products of its fermentation, raised several questions which 
rendered it advisable to make both an ultimate and proximate 
analysis of its tissues. Thus, if the growth of the weed in quantity 
is induced by pollution of the sea water by sewage, the weed itself 
might possibly be found to contain a higher proportion of nitrogen 
than is present in other seaweeds which luxuriate only in pure sea 
water. 
Again, as regards the products of its fermentation. What 
substance present in its tissues gives origin to the propionic and 
other acids ? Is it a carbo-hydrate ; and if so, what carbo-hydrate, 
and whence come the ferrous sulphide and sulphuretted hydrogen 
which are produced abundantly in the later stages of the fermenta- 
tion? 
Ultimate analysis. — Bor the ultimate analysis a considerable 
quantity of the seaweed was collected, and each frond separately 
washed in tap water, and finally with distilled water. The sea- 
