PUTREFACTION 78; 



filtration and found to induce the formation of carbonate of 

 ammonia from urea without the presence of bacteria. 



The ammoniacal fermentation of urea is of great importance, 

 for the latter substance, although it contains nitrogen, is of no 

 use as a source of this element for the nutrition of green plants ; 

 the ammonium carbonate produced is, however, useful in itself in 

 slight degree, and readily undergoes oxidation in the process of 

 nitrification (p. 789) in the ground, becoming thereby trans- 

 formed into nitrates, from which compounds green plants easily 

 obtain all the nitrogen they need. 



8. Putrefaction. — A considerable portion of the bodies of all 

 living animals and plants consists of complex nitrogenous com- 

 pounds, notably proteins. Unless special precautions are taken 

 to preserve them by cooking, embalming, or other means, these 

 bodies, after death, are attacked by various species of bacteria, 

 and the proteins and other substances are thereby decomposed 

 step by step into simpler compounds, several of which have a 

 disgusting odour. 



The term putrefaction is applied to these changes of nitro- 

 genous organic compounds, which are accompanied with the 

 evolution of foul-smelling products. 



In a great many instances the first step in the decomposition 

 of the proteins is the production of soluble albumoses and pep- 

 tones from them by the action of enzymes secreted by the 

 bacteria. Subsequently the peptones are split up into amido- 

 compounds, such as leucine and tyrosine, and these are in turn 

 broken down into still simpler bodies, the chief final products of 

 putrefaction being free nitrogen and hydrogen, ammonia, carbon 

 dioxide, sulphuretted hydrogen, methane, and other gases, which 

 escape into the surrounding air and soil. 



Not only do these changes take place in dead bodies of 

 animals and plants, but also in all products derived from them 

 and containing proteins, such as faecal matter, milk, cheese, and 

 all cooked flesh and tinned meats. 



