Whilst we do know something about the ability which most organisms possess of reproducing similar organisms, we cannot possibly say, from direct observation, that every organism which exists has had a similar mode of origin, because the cases in which organisms may have originated de novo are the very cases in which their mode of origin must elude our actual observation. Such a statement, too, would be all the more dangerous, in the face of the other analogy, when it can actually be shown that some organisms do make their appearance in fluids after precisely the same fashion as crystals.
Although, therefore, there is a contradiction between the unwarrantable and ill-begotten formula, “omne vivum ex vivo,” and the doctrines of what has been called “Spontaneous Generation”; there is no contradiction whatever between such doctrines and the only generalization which we are really warranted in arriving at, to the effect that some representatives of every kind of organism are capable of reproducing similar organisms.
Bacteria, Torulæ, or other living things which may have been evolved de novo, when so evolved, multiply and reproduce just as freely as organisms that have been derived from parents.
The views as to the origin of Bacteria and Torulæ which are most worthy of attention, may be thus enumerated:—
a. That they are independent organisms derived by fission or gemmation from pre-existing Bacteria and Torulæ.
b. That they represent subordinate stages in the life-history of other organisms (fungi), from some portion of which they have derived their origin, and into which they again tend to develop.
c. That they may have a heterogeneous mode of origin, owing to the more complete individualization of minute particles of living matter entering into the composition of higher organisms, both animal and vegetal.
d. That they may arise de novo in certain fluids containing organic matter, independently of pre-existing living things (Archebiosis).
I shall make some remarks concerning each of these views, though the evidence I have to adduce mainly concerns the possibility of the origin of Bacteria and Torulæ in the way last alluded to, viz., by Archebiosis.