1895 - 96 .] Mr Irvine and Dr Murray on Marine Muds. 37 
decreased in muds deposited at greater depth : thus at 500 metres 
1 c.c. of mud contains only 12,500 bacteria, whilst the water 
above contains only 22 per c.c. Russell’s investigations seem to 
show that the number of microbes decrease in a marked degree 
in the cooler waters of the Temperate Zone, whilst in the 
Mediterranean muds or slimes, where the water is warm even at 
great depths, they occur in very large proportion. 
It is to be observed that besides the organic matter carried to 
the sea from continents, and alga, one of the products of the sea, 
the remains of nitrogenous organic matter and effete products of 
animal organisms bulk largely in the fermenting or decomposing 
mass, and it is not at all the simple cellulose or alga with which we 
have to deal, as Professor Hartley argues is the case. It was there- 
fore impossible for us to give theoretical formulae such as is given in 
Professor Hartley’s paper, which would explain all the change 
taking place in these muds ; and, consequently, we adopted one 
which would give a general, and so far explanatory, view of what 
takes place. We were aware that the changes we endeavoured to 
point out in our paper were believed by some authorities to be 
simply the results of the ingestion or digestion of sulphates by 
bacteria, namely, bacterium hydro-sulfureum ponticum, and bac- 
terium sulfureum, which are supposed to be able to effect this 
change ; but at the time we brought this subject before the Society 
(1891) the then known facts in connection with these organisms, 
and the power they had ascribed to them, were of too vague and 
unsatisfactory a nature to be relied upon, and we chose rather to 
explain the facts resulting from our experiments in a manner as 
simple as was possible with known chemical data. Professor 
Hartley, in this connection, refers to Andrussow’s paper, read 
before the British Association at Edinburgh in 1892, “ On the 
Condition of the Water in the Black Sea under the 100 Fathoms 
Line ” ; but, so far as we know from personal communication with 
Andrussow and the meagre statement which appeared in the 
Royal Geographical Society’s Magazine, we incline to doubt that 
living organisms can exist in water which is practically a saturated 
solution of sulphuretted hydrogen ; but on this point we have no 
experiments of our own to bring forward. 
A reference is made to the “ bacterium hydro-sulfureum 
