CHAPTER XVIII. 



VITAL PHENOMENA OF NON-PATHOGENIC ORGANISMS. 



As has been stated in a former chapter, all putrefaction of 

 organic matter is associated with micro-organisms. It is now 

 generally admitted, because based on a large number of 

 exact experiments (by Schwann, Mitscherlich, Helmholtz, 

 Pasteur, Cohn, Burdon Sanderson, Lister, W. Roberts, 

 Tyndall, and many others), that organic matter kept safe 

 from becoming contaminated with micro-organisms of the 

 air, water, and filth, remains free of them, and consequently 

 of the form of decomposition which is generally considered 

 as putrefactive ; namely, the changing of proteids into soluble 

 peptones; then the splitting up of these into leucin and 

 tyrosin ; further the decomposition of these and other 

 crystallisable nitrogenous bodies into comparatively low 

 compounds. These in their turn by oxidation ultimately 

 yield ammonia, and its salts and nitrates of inorganic ele- 

 ments, with the simultaneous development of certain gases, 

 e.g. ammonia, sulphurreted hydrogen, and other products, 

 belonging to the aromatic series. The view now generally 

 entertained is that the organisms cause disintegration of 

 nitrogenous compounds by withdrawing from them certain 

 molecules of nitrogen, building up with these their own pro- 



