ZoBell — 56 — Marine Microbiology 



carbol-fuchsin or rose bengal. The bacteria and indigotin particles in lo 

 to 50 fields are counted under the oil immersion lens. By knowing the 

 number of indigotin particles present per gram of soil, one can calculate 

 the number of bacteria per gram of soil from the ratio of bacteria to 

 indigotin particles counted microscopically. 



The direct microscopic study of microorganisms in marine mud is 

 attended by numerous obstacles. Many of the microorganisms are sub- 

 microscopic in size or barely within the range of the resolving power of an 

 ordinary microscope. In many cases it is impossible to distinguish bac- 

 teria from particles of clay and organic detritus, and some of the bacteria 

 are obliterated by larger particles. At their best, direct counts on marine 

 mud are useful primarily for giving information ancillary to counts ob- 

 tained by cultural procedures. The latter are indispensable for evaluat- 

 ing the physiological activities of microorganisms. 



The significance of counting the number of microorganisms in a given 

 environment is often over-estimated. The population is merely an ex- 

 pression of the dynamic balance between the rate of production and the 

 rate of destruction of microorganisms. In appraising the role of micro- 

 organisms in chemical, geological, and biological conditions, the rate of 

 reproduction and activity of the microorganisms is a more important con- 

 sideration than is the number of microorganisms which may be present 

 at a given time. 



Benecke (1933) suggested adapting the method of Koffmann to the 

 study of bacteria in marine sediments or to those which are attached to 

 plankton organisms. After elutriating the soil with reagents selected to 

 separate the bacteria from particulate material and to disintegrate clumps, 

 the supernatant fluid in which the bacteria are suspended is decanted and 

 passed through an ultra-filter having a porosity of o.i ix. The residue is 

 stained with alcohol-soluble cyanosin for direct microscopic examination. 

 The success of such a method will depend upon the efficiency of the elutri- 

 ants in suspending bacteria and upon finding a satisfactory means of dis- 

 tinguishing bacteria from small particles of organic detritus. 



Submerged slide technic for studying bacteria in water : — Glass slides 

 and other sohd surfaces which are submerged in the sea soon become 

 covered with microorganisms. While studying the factors which influence 

 the fouhng of ships' bottoms, Hilen (1923) observed that the slime which 

 forms on surfaces submerged in the ocean is composed of a variety of bac- 

 teria as well as yeasts and molds. Naumann (1925) reported that, due 

 to their tenacious attachment, excellent preparations of iron bacteria may 

 be prepared by the submergence of glass shdes in iron-bearing waters. 

 Several other workers mentioned by ZoBell and Allen (1935) have sub- 

 merged slides and later examined them microscopically to follow the 

 distribution of sessile algae, diatoms, and other minute aquatic organisms 

 without attempting to detect bacteria. 



Henrici (1933) observed the attachment and growth of fresh-water 

 bacteria on submerged glass slides. Although Henrici recognized the 

 limitations of the submerged slide technic, he concluded that " the n.ethod 

 does offer a short cut towards an ecological survey of water bacteria." 

 Later Henrici (1936) observed a limited positive correlation between 

 plate counts and the number of bacteria found on slides submerged in 

 lakes. He recommended suspending slides 50 X 75 mm. in size in the 

 water for a few hours to a few days, depending upon the habitat. 



The attachment of bacteria, diatoms, actinomyces, and other micro- 



