28 Proceedings of Boy al Society of Edinburgh. [sess. 
(1) CaS0 4 + CH 4 = CaC0 3 + H 2 S + H 2 0. 
(2) CaC0 3 + H 2 S + 20 2 = CaS0 4 + C0 2 + H 2 0. 
These sulphur-bacteria are able to subsist on a very minute 
quantity of organic matter, and the only product of their “ respira- 
tion ” is sulphuric acid. This substance is formed by a process 
which is termed respiration, because it is the cause of a chemical 
change which sets free energy in the form of heat. The sulphur 
which the bacteria remove from sulphuretted hydrogen is secreted 
by the organism, and subsequently oxidised. 
As a matter of fact, the deoxidation of sulphates contained in 
either fresh or sea water is due to the action of such organisms as 
the bacterium sidyhureum and the bacterium hydrosuljphureum. 
In the Black Sea, as we know from the paper read by Dr 
Andrussow, a large amount of sulphuretted hydrogen is dissolved in 
the water. I certainly understood Dr Andrussow to say, at the 
meeting of the British Association at Edinburgh, that the process 
whereby sulphuretted hydrogen is formed is due to the bacteria, 
and I immediately connected this statement with the known re- 
duction of calcium and magnesium sulphates in both sea and fresh 
water by the sulphur-bacteria or beggiatose. 
But it appears, in the translated abstract of his paper in the 
Journal of the Royal Geographical Society, January 1893, to be 
attributed to the decomposition, after death, of a great number of 
minute organism and river debris. It is well known that the 
organic materials of dead organisms cannot decompose except by 
the operation of living organisms (Pasteur, Comptes Bendus, vol. 
56, p. 738). In Dr Andrussow’s diagram there are the following 
data : — 
“Lower Limit of Organic Life, 100 fathoms. 
Upper Limit of H 2 S, 100 fathoms. 
Upper Limit of Sulphides, 200 fathoms. 
No organic life except bacteria.” 
This certainly appears to bear out my interpretation of his remarks. 
There is, however, a note to the effect that the generation of H 2 S 
and of sulphides goes on down to a depth of 800 fathoms. 
It is now of no importance in what precise manner his remarks 
