1900-1901.] Prof. Letts and Mr Hawthorne on Ulva latissima. 281 
different species of micro-organisms, — the first producing fatty- 
acids together with hydrogen and carbonic anhydride ; the second 
causing the formation of sulphides. 
The evidence on this point was tolerably clear, for on several 
occasions no sulphides were produced at all, and, as a consequence, 
no blackening of the weed occurred, and no evolution of sulphur- 
etted hydrogen, although fermentation had been active, and fatty 
acids had been plentifully produced, together with hydrogen and 
carbonic anhydride. And in all our experiments in which the 
weed blackened, the acid-producing phase of the fermentation 
preceded that of the sulphide formation by a considerable interval. 
Also, when the ulva was allowed to ferment in tap water and 
not in sea water, the production of sulphides was always delayed, 
and very often did not occur at all. 
Numerous attempts have been made to isolate the organisms 
causing the two changes, but not with absolute success ; and we 
may take this opportunity to express our thanks to Dr Lorrain 
Smith and Dr Tennant for the assistance they have given us in 
this branch of the investigation. 
Stained preparations of the fermenting ulva showed that spore- 
forming bacilli similar in appearance to B. tetani were abundant, 
but all attempts to isolate them by Koch’s plate method or 
Esmarck’s roll tube (anaerobic) cultures, either with ordinary 
gelatine or agar media, failed, practically no colonies appearing. 
A special culture fluid was then made with sea water containing 
1 per cent, peptone and 1 per cent, glucose, and (after sterilisation) 
flasks of this were inoculated (A) with a droplet of the liquid from 
a tube containing fermenting ulva and sea water, and (B) with a 
minute fragment of the ulva itself from the same tube after its 
contents had been heated for twenty minutes to 80° C., to destroy 
all but spores. 
These cultures when incubated grew, and showed, it was 
thought, some signs of gas evolution. 
After five days agar plate cultivations were made from both, but 
no colonies appeared. Similar cultivations were made with a 
medium containing 1 per cent, peptone and 1 per cent, glucose with 
sea water and agar, both under aerobic and anaerobic conditions, 
but again without obtaining any definite growth of colonies. 
