Nitrogen-Metabolism on Land and in the Sea. 127 
electrical discharges in the air. 1 By far the most important method 
by which the nitrogen of the air is rendered available for plant use 
is, however, by means of the peculiar symbiosis between certain 
bacteria and leguminous plants. By this association large 
quantities of the nitrogen of the air are brought into combination, 
and on the death and decay of the plant are set free as nitrogen- 
compounds in the soil. 
The circulation of nitrogen in the sea must clearly take place 
on somewhat the same lines as on land. The constant presence 
of bacteria in the sea even down to considerable depths (about 
400 fathoms in the Atlantic) has been shown by Fischer’s work 
during the German Plankton-Expedition. Any dead animal or 
vegetable matter would thus soon be broken up into its constituent 
salts and so rendered available for the use of plants again. The 
presence also of nitrifying and denitrifying bacteria in the sea has 
been shown by Baur and Gran. The similarity between the 
circulation of nitrogen on the sea and on land is so far exact and 
there is thus a considerable and continual loss of nitrogen which 
escapes into the air. 
There must accordingly be some way of making up for the loss 
of nitrogen brought about by the denitrifying bacteria and also by 
the removal from the sea of nitrogenous material, such as fish. 
Two sources of combined nitrogen have been suggested. First 
the rivers, which, as mentioned earlier, bring down quantities of 
dissolved nitrogen-compounds; and secondly the sewage from 
large towns. Brandt believed that the loss could he largely 
supplied in this way. Reinke has pointed out, however, that it is 
very improbable that sufficient could be thus obtained even taking 
into account the small amount that would be returned in rain ; he 
held the view that probably there were organisms in the sea which 
could directly use free nitrogen in the same way as the bacteria in 
association with leguminous plants on land. 
The whole problem of the circulation of nitrogen in the sea has 
entered on a new phase through the discovery (due to Reinke’s 
initiative) by Benecke and Keutner of bacteria in the sea which 
have actually the power of converting free nitrogen into nitrogen- 
compounds. The two organisms observed, Clostridium Pasteurianum n 
' According to Knop one litre of rain-water contains about 0.9 
mgr. Ammonia. 
2 This organism was first discovered by Winogradsky in soil 
and was shown by him to live in symbiosis with two other 
bacteria and to have the power of using free nitrogen. 
