114 MICRO-ORGANISMS IN WATER 



Thus the nearest point to the land at which a 

 sample was taken was 4 kilom., where the sea had a 

 depth of 75 metres, and hence the chance of any dis- 

 turbance in the normal bacterial contents of this sea- 

 water from accidental contamination from the shore is 

 very slight ; and even if any such source of error should 

 arise, it would at most be only likely to take place 

 during or after violent storms blowing from the coast. 



Examination of sea-mud revealed the presence of 

 very large quantities of bacteria. It was found, how- 

 ever, that the numbers steadily diminished up to a 

 certain point with the greater depth at which the 

 samples were abstracted, this being especially noticeable 

 in the immediate vicinity of the coast. After 250 m. 

 and up to 1,100 m. no further important reduction 

 was observed. 



Number of Bacteria found at various depths in 1 c.c. of sea-mud 

 and 1 c.c. of sea-water respectively (Russell) 



Depth in metres 



50 

 85 

 100 

 140 

 200 

 250 

 300 

 400 

 500 

 825 

 1,100 



1 Russell states that these higher figures must not necessarily be regarded as indicating 



a larger number of bacteria as being present at the greater depth, but are to be attributed 

 rather to slight local variations, as the samples were collected over as wide an area as possible. 



As regards the varieties of organisms present, it was 

 ascertained that more than half appeared only to belong- 

 to this mud, and were not discoverable in the sea-water 

 itself; three individual microbes in particular were 

 especially characteristic of this mud, as much as 35 

 per cent, of the total number of colonies found on 



