186 Marine Microbiology 



end of the experiment^ (Table 3). During the term of the ex- 

 periment the total number of cells remained nearly constant. 

 After eight days of washing out with sterile water, the columns 

 contained still a remarkable number of cells. The relation to 

 the size of the cells and of the grains in the sediments is recog- 

 nizable here also. Serratia chfters as to the low number of cells 

 which are retained under limnic conditions, compared with the 

 high numbers of strain H/8b. 



SUMMARY 



Model experiments with five species of bacteria and two 

 types of sandy sediments have shown that transportation of cells 

 through the sediment, washing out, and distribution in different 

 layers of the sedimentary column were in general influenced by 

 the size of tlie cells and the size of the grains of the sediment. 

 Under marine conditions (suspensions of cells in seawater) a 

 higher number of cells were retained than under limnic con- 

 ditions. Besides the physical laws which regulate retention and 

 elution, specific factors bound to single species of bacteria were 

 effective. After eight days of washing out, the sediments still con- 

 tained changing numbers of living bacteria. 



2 (b), (c) and (d) in per cent of (a). Calculation of (b) and (c) from cell 

 contents and quantities of dropping water. The estimation of (d) is only 

 approximate from the cell contents of five samples of 300 cm^ of sand apiece 

 (total volume of sand in a column 1,500 cm^). 



