Structure, Growth and Distribution. 13 



vegetables. Alkalies, as ammonia, may be produced as. 

 in the fermentation of urine in the horse stable. Highly 

 poisonous substances are sometimes formed in the bodies 

 of animals by the disease-producing bacteria. 



Distribution of bacteria. Bacteria are more univer- 

 sally distributed than any other form of life. They be- 

 come very abundant where conditions for growth are 

 suitable, particularly where a fitting supply of food i 

 fcund. The soil is teeming with germ life, for the dead 

 tissues of both plant and animal life find their way to 

 the soil. As most of this material is found in the upper 

 part of the soil, the bacteria are naturally more abund- 

 ant here than in the subsoil. Some of the kinds occur- 

 ring in the soil are quite indispensable to the life of 

 higher plants, since they aid in the preparation of the 

 food for plants. 



Next to the soil, the intestinal canal of animals sup- 

 port a large and varied bacterial flora. The blood, th& 

 different internal organs such as the liver and spleen, 

 or the muscles contain few or no bacteria, but in the 

 alimentary tract from the mouth to the rectum, bacteria 

 are found in varying numbers. 



Water is also to be looked upon as one of the natural 

 habitats of bacteria, for it always contains food sub- 

 stances in greater or less abundance. As a rule the 

 number of bacteria in water depends on the relation of 

 the water to the soil. Surface streams usually contain 

 many bacteria, especially when the water from culti- 

 vated fields drains into the stream. In shallow wells 

 that receive the drainage from the upper layers of the 

 soil, bacteria also abound. As the water percolates 

 through the soil the bacteria are filtered out, hence, the 

 water from deep wells contains very few. The number 



