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 decom- 

 position 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 elements, with the simultaneous 

 development of certain gases, e.g. ammonia, sulphuretted 

 hydrogen, and other products, belonging to the aromatic series. 

 The view now generally entertained is that the organisms 

 cause disintegration of nitrogenous compounds by withdraw- 

 ing from them certain molecules of nitrogen, building up with 

 these their own protoplasm. Similarly carbohydrates and 

 inorganic salts, as phosphates, potassium, and sodium salts, 

 are dissociated by them, inasmuch as they require a certain 

 amount of carbon, phosphorus, potassium, and sodium, for 

 building up their own bodies. In this process of decomposition 

 certain alkaloids are produced, the composition of which is not 

 accurately known, and which are called by the collective name 

 of ptomaines (Selmi and others). These alkaloids are known 

 to have a poisonous (toxic) effect when introduced in sufficient 

 quantities into the system of a living animal. Very possibly 

 the poisonous property of some articles of food, that have 



