1900-1901.] Prof . Letts and Mr Hawthorne on Ulva latissima. 283 
Two colonies from No. 1 and four from No. 2 were planted out 
in tubes containing fragments of ulva and sea water previously 
sterilised. In three days the tubes inoculated with No. 1 had 
given off a good deal of gas, and one of those inoculated with No. 
2 had also given off gas and its contents were turbid. It seems 
probable, therefore, that by this method the organism causing the 
acid fermentation was isolated. 
Regarding the second or sulphide-forming phase of the fer- 
mentation, as we have already said, it always occurred much later 
than the first or acid phase, and frequently did not take place at 
all ; and although the presence of sea water does not appear to be 
absolutely essential to its occurrence, yet undoubtedly it materially 
assists it, and for that reason we are inclined to believe that the 
sulphides owe their origin chiefly to sulphates in the water, and 
possibly in the ulva itself, and not to the albuminoids present in 
such abundance in the weed. 
There is also some evidence to show that the organisms con- 
cerned in the process occur in the mud of the foreshore where the 
ulva is found, and not in the sea water. 
The following experiment brings out these facts. 
A number of test-tubes were partly filled with sea water, and 
others with tap water, and in each a piece of ulva was placed 
previously well washed in tap water, and all air bubbles adhering 
to the weed were got rid of by pressure with a glass rod. 
A cotton- wool plug was then inserted in the mouth of each tube, 
which was made to support a strip of paper moistened with lead 
acetate, which hung about an inch above the surface of the liquid. 
In addition to five such tubes containing the washed weed and 
sea water, and five containing the washed weed and tap water, two 
similar tubes were prepared containing unleashed weed, one with 
sea water and the other with tap water. All the tubes were then 
placed in the incubator. In 24 hours the acid phase of the 
fermentation had commenced in all the tubes, indicated by the 
inflation of the weed by the evolved gases. 
In 48 hours the lead paper in the tube containing the unwashed 
weed and sea water had begun to blacken distinctly, and that 
containing the unleashed weed and tap water was also tinged, 
though faintly. In 72 hours the lead papers in all the sea water 
