444 BACTBBIOLOGY. 



■overlying water is largely due to the fact that certain bac- 

 teria can live and multiply in the slime. Fully one-third of 

 the bacteria present in the slime belonged to three species 

 which were met with only in this material. Certain species 

 of slime bacteria found at Naples at a depth of 3,500 feet 

 were also met with at Wood's Holl, near the coast as well as 

 at a distance of 100 miles. It is of interest to note that 

 Fischer obtained no bacteria from slime gathered at a depth 

 -of 1-3 miles. 



Sewage water, necessarily, is very rich in bacteria. 

 Usually, a drop will be found to contain several hundred 

 thousand. The sewage water in large cities like Paris and 

 London is known to contain as many as 6 or 8 millions of 

 bacteria per c.c. The water in the public washing stations 

 which float in the Seine at Paris was found to contain from 

 12 to 40 millions of bacteria in a c.c. 



Soil. 



The upper layers of the soil contain enormous numbers 

 /of bacteria which play a most important part in the econ- 

 omy of nature. As indicated in Chapter V (p. 112), the dead 

 animal and vegetable matter deposited upon the surface of 

 the earth is sooner or later broken up into the simplest of 

 inorganic compounds, — carbonic acid, water, ammonia, 

 nitrous and nitric acids, hydrogen sulphide, etc. This is 

 done through the agency of the bacteria in the soil. With- 

 out their presence and activity, the dead matter wonld re- 

 main as such, and would accumulate as layer on layer. 

 The nitrogen of the protein matter which is contained in the 

 protoplasm of animal and plant cells is derived from the in 

 organic nitrogen of the soil. Were it not for the bacterial 

 activity carried on in the soil this supply of inorganic nitro- 

 gen would in time become exhausted, and, as pointed out by 

 Pasteur, life would soon cease to exist, 'fhe dead plant and 



