260 BACTERIA IN THE SEA [PART III 



produced as part of the surplus energy of the organism. In the 

 case of the bacteria it is arrested by withdrawal of the oxygen 

 supply, and is increased by the abundant supply of the latter, 

 and also by the supply of some highly combustible food such as 

 carbohydrate. In all cases the light is greenish blue in colour. 



The nearest terrestrial allies of the halibacteria are the cholera 

 bacillus and its congeners. In these two groups of micro-organisms 

 the appearance of the colonies to the naked eye is similar, and the 

 morphology and biology are the same, or are very similar. The 

 cholera germ is a typical fresh water microbe. Fischer points out 

 that the spirallar form is the best adapted for progression through 

 water or for suspension in the latter. 



In what numbers are these bacteria present in the sea ? 

 Fischer estimated that from 20 to 785 germs were present per c.c. 

 of the water from the Sargasso Sea in the mid Atlantic. In the 

 Gulf Stream 645 bacteria were counted in 1 c.c. on one occasion. 

 If we take it that about 600 germs are in 1 c.c. then we have a 

 total of 600 millions per cubic metre of sea. I do not doubt that 

 this is a reasonable estimate, and that it is vastly exceeded in the 

 water from inshore areas. But prodigious as are the numbers, they 

 represent only a very small mass of life. Thus 600 millions of 

 bacteria form far less than one gram of solid substance. 



The putrefactive bacteria. We may now consider some 

 groups of marine bacteria which have special modes of life, and the 

 importance of which lies in the manner in which these organisms 

 affect the abundance of the ultimate sources of food stuffs in the 

 sea and on the land. Those germs which we have been considering 

 so far are concerned with the breaking down of dead organic 

 matter, that is we call them putrefactive bacteria. This leads us 

 to a more minute consideration of the modes of nutrition of these 

 micro-organisms. Fischer divides all the bacteria into three main 

 divisions according to their habitat and mode of nutrition. These 

 are : 



(1) The prototrophic bacteria. These are the most lowly 

 organised of living things. They can use as sources of food such 

 very simple substances as nitrates and nitrites, carbon dioxide, 

 sulphuretted hydrogen and even elementary nitrogen. Green plants 



