174 
NATURE 
[Sune 30, 1870 
som2 of the simplest Amada, after they have encysted them- 
selves. In all these cases, formless and apparently homogeneous 
or merely granular living matter, resolves itself more or less 
rapidly into a number of individualised segments, which are 
Fic. 4.—Representing subdivision of formless living matter within encysted 
Protomyxa, and exit of products from cyst as active tailed Zoospores, 
ch subsequently become converted into reptant Amozbz (Haeckel). 
capable of existing as independent living things.* These 
changes occur in the formless matter of definite organisms, and 
the products of subdivision tend to reproduce organisms of a 
similar kind ; but the changes which take place in portions of 
the pellicle are changes occurring in fortuitously aggregated 
living matter, and the resulting products are, as might have been 
expected, more variable in kind. There is every reason to 
believe that the changes which take place in the homogeneous 
living matter of the encysted Protomyxa occur by reason of the 
molecular properties of this living matter, and are not occa- 
sioned by any occult influence exercised by the mere inert 
cyst-wall, which is but a product of the living matter that it 
Fic. 5.—Showing the mode of origin of motile Zoospores within the terminal 
dissepiment of Ach/ya (Tulasne). 
encloses. And so we have good reason for supposing that the 
changes which take place in the mere granular mucilage of 
the rapidly-formed terminal segment of an 4chlya, by which this 
in the space of less than two hours resolves itself into free- 
swimming zoospores, is to be ascribed to the molecular proper- 
ties of the mucilage itself which undergoes the change. In the 
pellicle, on the other hand, we have an aggregation of granular 
living matter also, and the observations which I have adduced 
simply go to show that those molecular properties of living matter 
* All this part of the subject will be much more fully treated in the work 
on The Beginnings of Life. The possession or not of the property of motility 
seems to be an altogether unessential characteristic. ‘The products of sub- 
division of such an encysted Amada as Protomyxa aurantiaca are motile 
zoospores, and so are those of the fungoid Achlya prolifera; but the repro- 
ductive products arising from the subdivision of the formless matter within 
the spore-cases of Pezize and other fungi are motionless, and this is the case 
also with the gonidia of the Safrolegnie, which are fungoid organisms, other- 
wise almost undistinguishable from Achlya, 
which lead to its differentiation and further organisation, are not 
limited to the living matter that is contained within organisms 
of a definite type. Just as the changes which take place in the 
structureless living matter of these organisms seem to be due to 
the forces acting upon, and to the reactions amongst, the several 
molecules of which it is composed, so do the changes which 
occur in given areas of the pellicle seem referrible to the in- 
fluence of physical forces upon the living molecules of which 
it is composed, and upon the mutual inter-action of these upon one 
another when under the influence of such incidence. In both 
cases the changes take place in living matter ; in both cases they 
are the results of molecular activity : in the one set of cases they 
take place in a fortuitous aggregation of living matter, and the 
products are accordingly very variable in nature, whilst, in the 
other set of cases, just as they take place in living matter which 
constitutes part of a definite organism, so are the products more 
definite in kind. 
But this process, which most certainly occurs in the living matter 
of a pellicle, is of a kind not hitherto generally recognised as one 
of the modes by which unicellular organisms, or spores of fungi, 
may originate, These are, in fact, instances of what has been 
called ‘‘ spontaneous generation,” or what we may better term 
heterogenous evolution. The majority of biologists would be as 
much inclined to believe that these processes did not take place 
as they are inclined to disbelieve that a monad or a bacterium 
may be born de zeve in a solution of organic matter. The oc- 
currence of the one process has been thought to be about as im- 
probable as that of the other. Yet the one can be seen un- 
doubtedly taking place with the aid of the microscope alone. 
Unfortunately, however, the organic molecules, which are sup- 
posed to coalesce in the solution of organic matter, in order to 
form the smallest visible Living particle, are themselves invisible. 
We cannot, therefore, trace the genesis of one of these particles 
with the aid of the microscope, any more than we are able to trace 
the genesis of a crystal beyond its minimum visible stage. In the 
one case physicists and biologists willingly assume that such 
ultimately visible particles are the products of a ‘*spontaneous ” 
coalescence of molecules, which are themselves invisible, whilst 
in the case of organisms they will grant no such assumption. 
They require us to prove, in fact, that such organisms have not 
been produced from pre-existing though perhaps invisible 
‘* germs,” before they will grant for organisms that probability 
which they at once concede in the case of crystals. ‘This differ- 
ence which is made between the two cases seems due, in great 
part, to some theoretical views which are held concerning the 
nature of Life. And yet it would not be difficult to show that 
the metaphysical or vitalistic theories in question, to which they 
commit themselves, are directly opposed to some of the most 
accredited scientific doctrines of the day.* The doctrine of the 
Conservation of Energy and of the Correlation existing between 
the Vital and the Physical forces do, if pushed to their ultimate 
issues, inevitably bring us to the conclusion that the forces acting 
within all Living bodies are molecular forces, and that such forces 
are derived from the physical forces of the outside world just as 
surely as the matter of the organism formerly existed outside 
itself. The most careful interpretation of scientific evidence, 
moreover, would lead us to the conclusion that what is called 
the Life—or in other words the aggregate set of phenomena dis- 
played by one of the simplest bodies which we call a living 
thing—is as much the essential and inseparable attribute of the 
particular molecular collocation which displays it, as the proper- 
ties of the crystal are essential to the kinds and modes of aggre- 
gation of the molecules which enter into its composition. It may 
be maintained, therefore, that all @ priori presumptions, based 
upon the best scientific evidence, would lead us to disbelieve the 
‘*vitalistic” theories which are still held by many at the present 
day. Itisthe vitalist, however, who alone has any logical reason 
for ins.sting that what may be a good and valid mode of 
accounting for the origin of crystals cannot be considered to 
hold good in the case of organisms. Those who believe 
that the forces acting in Living things manifest themselves 
in the individual molecules of which these are composed, 
and that such forces are convertible with the ordinary 
physical forces, have, on the other hand, strong @ frioré rea- 
sons for believing that Life will manifest itself wherever 
particular collocations of complex organic molecules occur. It 
rests, then, in reality, with the vitalist, who assumesthe truth of a 
mere theory, in favour of which he can adduce no scientific 
evidence, to show why a different rule should be presumed to 
* This I shall attempt to show fully elsewhere. 
