MICROBES, MOULDS, AND YEAST. 1 99 



they keep the human species up to a proper standard 

 by destroying the unfit. 



The number of bacteria varies according to the 

 situation and character of the soil itself. A cubic centi- 

 metre of arable land will contain from 2-15 millions 

 of bacteria and an ounce of roadside dust will probably 

 contain some 50 millions. Bacteria have been found 



Fig. 25. — Bacteria, (i) Micrococcus. (2) Streptococcus. (3) Bacterium. 

 (4) Sarcina. (5) Pseudomonas. (6) Bacillus. (7) Spirillum. (8) Bacillus. 

 (9) Spore of B. subtilis. (10) Spore of B. megatorium. (11) Clostridium. 



even at a depth of 50 centimetres (nearly 20 inches) 

 below the surface. Water contaminated by sewage 

 is full of bacterial germs. No less than 49 distinct 

 species have been extracted from London sewage 

 water. Cream left standing for 36 hours may develop 

 485,000,000 bacteria per cubic centimetre. 



Bacteria are a distinct group of Fungi easily recognised 

 by their exceedingly minute size and characteristic 

 appearance. The name Schizomycetes {division fimgi) is 

 derived from one of their most distinctive characteristics. 

 They are one-cell plants and multiply by division. 

 Each cell divides into two daughter cells ; and these 

 very soon become mature bacteria capable of dividing 



