10 GENERAL PART. 



organised bodies. They relate (1) to the mode of origin, (2) to the' 

 mode of maintenance, (3) to the form and structure of the organism. 

 Living bodies cannot be manufactured by physico-chemical means 

 from a definite chemical mixture under definite conditions of warmth, 

 pressure, electricity, etc. ; their existence rather presupposes, accord- 

 ing to our experience, the existence of like or at least very similar 

 beings from which they have originated. It appears that, in the 

 present state of our knowledge, there is no evidence to show that an 

 independent abiogenetic generation (generatio cequivoca, spontaneous 

 generation) actually takes place, even in the simplest and lowest forms 

 of life : although very recently some investigators (Pouchet) have 

 been led by results of remarkable but equivocal experiments to the 

 opposite view. The existence of the generatio cequivoca would offer 

 a very important service to our contention for the physico-chemical 

 explanation ; it even appears to be a necessary postulate in order to 

 explain the first appearance, of organisms. 



The second and most important characteristic of organisms, and 

 that on which the very maintenance of life depends, is their metabolic 

 power, i.e., the power which they possess of continually using up and 

 renewing the matter composing the body. Every phenomenon of 

 growth presupposes the reception and change of material constituents ; 

 every movement, secretion, and manifestation of life depend on the 

 exchange of matter, on the breaking down and building up of 

 chemical compounds. On this alternating destruction and renewal 

 of the combinations of the body substance two properties necessary 

 to living things depend, viz., the reception of food and excretion of 

 waste products. 



It is the organic substances (so called on account of their occurrence 

 in organisms), i.e., the ternary and quaternary carbon compounds (the 

 former composed of carbon, hydrogen, and oxygen, the latter of 

 these with the addition of nitrogen, and among the latter are 

 included the albumins) which undergo the exchanges characterising 

 metabolism ; they either (in animals) break up under the influence 

 of oxidation into substances of simpler composition ; or (in plants) 

 are built up by substitution from simpler inorganic substances. 

 But just as the general fundamental properties (elasticity, weight, 

 porosity) of organisms agree so closely with those of inorganic bodies, 

 that it was possible to construct a general theory of the constitution 

 of matter, so all the elements (fundamental substances which differ 

 qualitatively, and are chemically incapable of further simplification) 

 of organic matter are again found in inorganic nature. A vital 



