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 



IVLicrobial Pofulation 



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

 on the average, of 5 to 20 per cent bacterial cells. Lissauer (575) 

 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 9 to 42 per cent of the bulk of animal stools, the 

 percentage depending on the composition of the foodstuffs, the nature 

 of the animal and its condition of health, and other factors {^66). 

 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. 



By suitable methods of cultivation, human feces were found (626) 

 to contain 18 billion bacteria per gram. About 100 billion bacteria may 

 be produced daily in the human intestine. Human feces are made up, 

 on an average, of 32.4 per cent bacterial cells amounting to 2,410 

 million bacteria per milligram of moist material. Feces of healthy 



