20 HUMAN AND ANIMAL WASTES 



produced J various mineral compounds, such as phosphates, sulfates, and 

 potassium salts are also liberated. These mineralized substances are es- 

 sential for the continuation of plant and animal life on this earth. 



Largely because of the activities of the microorganisms inhabiting 

 soils and water systems, man does not need to worry about the disposal 

 of plant and animal wastes. These activities need only be regulated, in 

 order to accomplish the breakdown of complex substances with the 

 greatest efficiency and the least loss of valuable nutrient elements. The 

 following principal objectives are usually to be attained: first, the de- 

 struction of plant and animal pathogens, including pathogenic bacteria 

 and fungi and disease-producing protozoa, worms, and insects j second, 

 the liberation of the essential elements required for plant nutrition in 

 available forms, especially carbon, nitrogen, and phosphorus j and, 

 third, the formation of certain resistant organic substances, known col- 

 lectively as humus, which are essential for the improvement of the 

 physical, chemical, and biological condition of the soil. 



STABLE MANURES AND FECAL RESIDUES 



Microbial Population 



Fresh excreta of animals and man are rich in fecal bacteria, consisting, 

 on the average, of 5 to 20 per cent bacterial cells (802). Lissauer (533) 

 calculated that the bacterial substance of feces ranges from 2.5 to 15.7 

 per cent of the dry weight, with an average of 9 per cent. Bacteria were 

 reported to make up as much as 9 to 42 per cent of the bulk of animal 

 stools, the number depending on the composition of the foodstuffs, the 

 nature of the animal and its condition of health, and other factors (364). 

 Since i mg. of dry bacterial substance contains about 4 billion bacterial 

 cells, the number of these organisms in fecal excreta can be seen to be 

 very large, although many, if not most, of the cells are no longer in a 

 living state. Osborne and Mendel (659) removed from the feces of 

 white rats the residual food material and found that the bacterial cells 

 made up 23 to 41 per cent of the total material j the nitrogen content of 

 these cells varied from 10.7 to 12.2 per cent. Since the removal of the 

 residual foodstuffs consisted in treatment with ether, alcohol, and acid, 

 some of the bacterial cell constituents were also removed j the actual 



