554 Marine Microbiology 



our attention was drawn to stations 29 and 30, lying close to the 

 mouth of the Nile. Here the largest numbers of heterothrophs 

 were obtained and large numbers were observed over the whole 

 water mass. It leads one to expect that the Nile waters penetrate 

 into the open sea for at least 40 miles, and that the main stream 

 of water goes in a north-west direction. If one takes into consider- 

 ation that the stations were occupied in September when the Nile 

 was in high flood ( 14 ) and as a consequence, the maximum run- 

 off is taking place, a considerable development of bacterial life is 

 possible, perhaps indicating its influence upon almost all tlie 

 horizons (except 150 and 750 m) at the deep-water station 388 

 ( 123 miles from the mouth of the Nile ) . The central part of the 

 Mediterranean Sea and the Ionian Sea are deficient in saprophytic 

 bacteria compared with the above mentioned seas, judging by the 

 frequence of occurrence of samples giving low counts. Thus the 

 colony count from to 10 occurs in 33.7 per cent and 32.5 per 

 cent of the samples; 31.2 per cent and 33.6 per cent had counts 

 from 11 to 100 bacteria; and approximately the same percentage 

 (33% and 33.6%) had from 100 to 2500. Thus these seas are ap- 

 proximately equal in numbers of heterotrophic bacteria. In the 

 Ionian Sea, stations 18 and 19, situated close to the Otranto 

 Strait, gave the highest bacterial counts; in the central part of 

 the Mediterranean, the shallow stations 342, 350 and 335, lying in 

 the regions where the Atlantic waters make their influence felt, 

 yielded the largest number of colonies. 



In the deep water stations a sharp increase in bacterial 

 counts at great depths, up to 2500-3500 m, have been observed. 

 In some regions of the Mediterranean Sea, the number of hetero- 

 trophic bacteria in the depths often considerably exceeds the 

 number found in the layer of photosynthesis. According to Bul- 

 jan's hypothesis, submerged eruptions of volcanoes in the Tyr- 

 rhenian Sea are of great importance to the enrichment of deep 

 waters. From these sources, nutrients are carried by currents all 

 over the Mediterranean Sea, and this is partly the reason for the 

 greater development of phytoplankton at great depths ( 15 ) . 

 Hence the richness of bacterial life in the deep water regions of 

 the Mediterranean basin becomes clear. As far as it is possible to 

 judge from the three stations occupied, the Sea of Crete has the 



