148 RECENT RESEARCHES 



there may have beeft this Hne of continuity, we cannot say that it 

 exists at the present time ; that spontaneous generation is no 

 discovered part of Nature's processes ; but that " the properties of 

 living matter distinguish it absokitely from all other kinds of things," 

 and that the facts to-day in the hands of the biologist " furnish us 

 with no link between the living and the non-living." They say 

 that as the whole analogy of Nature supports the aphorism of 

 Harvey — Om?ie vhmm e vivo — that as every existing living animal, 

 as far as we know, is evolved from a pre-existing animal of the 

 same species, and as every plant is developed from a pre-existing 

 similar plant, so with the Bacteria, we have every reason to suppose 

 that they are always developed from pre-existing individuals of the 

 same organisms. 



The proofs relied upon by the advocates of the former theory 

 are chiefly the following : — It is argued that as the adult Bacteria 

 are killed at a given temperature — much below the boiling point 

 of water — if an infusion is boiled with every possible precaution, 

 and while boiling hermetically sealed, and if, after a lapse of time, 

 the vessel is opened, and found to contain Hving organisms, they 

 must have arisen de novo; that is, the non-living have produced 

 the living. 



The opponents of this theory, on the contrary, say, that the 

 difficulties and possible errors in such experiments are unbounded ; 

 that while the adult Bacteria are destroyed by a moderate temper- 

 ature (say 140^ F.) the spores can bear a much greater amount of 

 heat,(even exposure to as high a temperature as 260° F., or possibly 

 more than this), without losing their vitality ; and that if an organic 

 infusion is subjected to a sufficient amount of heat, with due 

 precautions to prevent any possible source of error, it may be 

 absolutely sterilised : and if then hermetically sealed, as long as no 

 air is admitted, or only air deprived of its organic particles, no 

 life is ever developed. 



It is to Tyndall that we are indebted for a series of beautiful 

 experiments in support of the foregoing conclusions. We all 

 know the effect of a beam of sun-light or other concentrated ray 

 passing through the air, how it reveals to us the numerous dancing 

 motes which are invisible in ordinary light, and are even so 

 exquisitely minute as to be beyond our highest microscopical 



