44 Marine Microbiology 



ted from decaying sea weed, and on it tests were made to assay 

 the effect of progressive withdrawal of nitrogen on the popula- 

 tion level. The somce of nitrogen was asparagine and the carbon, 

 source, lactate, was kept in surplus. The technique was to take a 

 flourishing colony of Spirillum and prefuse it with dilute medium 

 until the population declined to a new lower plateau; then a fur- 

 ther dilution was applied and so on until a wash-out of the entire 

 colony occurred with (in theory) eventual extinction. In this way 

 it was possible to establish the relation of the level of nitrogen to 

 tlie population which could be supported. Unfortunately, efforts 

 to extend the method to natural sea water have so far been un- 

 successful. Neither the polluted water of Naples harbour nor off- 

 shore water would serve unless supplemented with pieces of sea 

 weed and nutrients. Thus, tliis promising technique may require 

 the selection of some other test organism before it can yield 

 direct measurements on natural productivity. 



Turning to another topic, it is well known that although 

 great numbers of bacteria enter the ocean by way of surface 

 drainage and sewage outfalls, a rapid decrease occurs as one 

 proceeds outward from land. It has also been reported that the 

 most important factor contributing to the decline is the bacteri- 

 cidal action of the water. Pramer and colleagues (Chapter 52) 

 dealt with the phenomenon, repeatedly observed, that this bac- 

 tericidal action of sea water tends to be abolished by autoclaving. 

 In a typical experiment by Pramer et al., the survival of E. coli was 

 followed in untreated control, in filtered and in autoclaved sea 

 water. In all six tests, autoclaving greatly increased the number 

 of survivors. Membrane filtration also promoted survival, though 

 to a lesser extent. 



Working in the same field, Jones (Chapter 53), reported on 

 the terminal growth of several organisms. Normal sea water, sup- 

 plemented with a complex medium was quite inhibitory, more so, 

 for example, than 16 units of penicillin G per ml to susceptible or- 

 ganisms in artificial sea water. The inhibitory effect varied con- 

 siderably with place of collection and deptli; samples adjacent to 

 the bottom were more toxic than those near the surface. Toxicity 

 declined gradually with storage. The general conclusion from 

 both papers is that the inhibiting effect resides with inorganic salt 



