the not living. Since the earth, and with it the conditions under which

alone life is possible, have had a beginning in time, life upon the earth

must also have had a beginning. The assumption that the first living

organisms may have come to the earth on meteorites simply shifts the

problem a step farther back, for according to all current theories of the

universe, if there are in any of the heavenly bodies conditions admitting

of the presence of life, these conditions have arisen from others in which

life was impossible. Therefore, since this suggestion is on the face of it

a mere evasion of the difficulty, the theory of spontaneous generation

naturally arose. There is something almost comical in the change in the

attitude of the natural sciences to this theory. For centuries it was one

of the beliefs of popular superstition, with its naive way of regarding

nature, that earthworms "developed" from damp soil, and vermin from

shavings, and in general that the living arose from the non-living. On the

other hand it was one of the characteristics and axioms of scientific

thought to reject this naive generatio equivoca, and to hold fast to the

proposition, omne vivum ex ovo, or, at least, omne vivum ex vivo. And

it was regarded as one of the triumphs of modern science when, about the

middle of the last century, Pasteur gave definiteness to this doctrine,

and when through him, through Virchow, and indeed the whole younger

generation of naturalists, the proposition was modified, on the basis of

the newly discovered cell-theory, to omnis cellula ex cellula. But a

short time after Pasteur's discoveries, the ideas of Darwinism and the

theory of evolution gained widespread acceptance. And now it appeared

that, in rejecting the theory of generatio equivoca, naturalists had, so

to speak, sawn off the branch on which they desired to sit, and thus many,

like Haeckel, became enthusiastic converts to the theory which natural

science had previously rejected.



Constructing theories and speculations as to the possibilities of

spontaneous generation is regarded by some naturalists as somewhat

gratuitous (cf. Du Bois-Reymond). In general, it is regarded as

sufficient to point out that the reduction of the phenomena of life as we

know them to those of a simpler order, and the unification of organic and

inorganic chemistry, have made the problem of the first origin of life

essentially simpler, and that the law of the constancy and identity of

energy throughout the universe permits no other theory. But others go more

determinedly to work, and attempt to give concrete illustrations of the

problem. The most elementary form of life known to us is the cell. From

cells and their combinations, their products and secretions, all

organisms, plant and animal alike, are built up. If we succeed in deriving

the cell, the derivation of the whole world of life seems, with the help

of the doctrine of descent, a comparatively simple matter. The cell itself

seems to stand nearer to the inorganic, and to be less absolutely apart

from the inanimate world than a highly organised body, differentiated as

to its functions and organs, such as a mammal. It almost seems as if we

might regard the lowest forms of life known to us, which seem little more

than aggregated homogeneous masses of flowing rather than creeping

protoplasm, as an intermediate link between the higher forms of life and

the non-living. But the theory does not begin with the cell; it assumes a

series of connecting-links (which may of course be as long and as

complicated as the series from the cell upwards to man) between the cell

and matter which is still quite "inorganic" and which is capable only of

the everyday chemical and physical phenomena, and not of the higher

syntheses of these, which in their increasing complexity and diversity

ultimately come to represent "life" in its most primitive forms. As

proteid is the chief constituent of protoplasm, it is regarded as the

specific physical basis of life, and life is looked upon as the sum of its

functions. And it is not doubted that, if the conditions of the universe

brought about a natural combination of carbon, hydrogen, nitrogen and

oxygen in certain proportions, so that proteid resulted, the transition to

proteid which forms itself and renews itself from the surrounding

elements, to assimilating, growing, dividing proteid, and ultimately to

the most primitive plasmic structure, to non-nucleated, nucleated, and

finally fully formed cells, could also come about.



Haeckel's demonstration of the possibility of spontaneous generation is

along these lines. He refers to the cytodes, the blood corpuscles, to

alleged or actual non-nucleated cells, to bacteria, to the simplest forms

of cell-structure, as proofs of the possibility of a descending series of

connecting-links. He (and with him Naegeli) calls these links, below the

level of the cell, Probia or Probions, and for a time he believed that he

had discovered in Bathybius Haeckeli presently existing homogeneous

living masses, without cell division, nucleus or structure, the "primitive

slime" which apparently existed in the abysmal depths of the ocean to this

day. Unfortunately, this primitive slime soon proved itself an illusion.



Opinions differ as to whether spontaneous generation took place only in

the beginning of evolution, or whether it occurred repeatedly and is still

going on. Most naturalists incline to the former idea; Naegeli champions

the latter. There are also differences of opinion as to whether the origin

of life from the non-living was manifold, and took place at many different

places on the earth, or whether all the forms of life now in existence

have arisen from a common source (monophyletic and polyphyletic theories).