172 
case we have to do with crysta/lisable matter, in solution, 
and in the other with those big-atomed, unstable compounds 
which constitute the so-called co//ofdal states of matter. And 
itis well to call attention to the fact that, concerning these 
latter states, the late Professor Graham, one of the most 
cautious and philosophical of chemists, wrote :*—‘* Another 
and eminently characteristic quality of Colloids is | their 
mutability. Their existence is a continual metastasis. . . 
... The Colloidal is, in fact, a dynamical state of matter, the 
crystalloid being the statical condition. The colloid possesses 
Enercia. Jt may be looked upon as the probable primary source 
of the force appearing in the phenomena of vitality. To the gradual 
manner in which colloidal changes take place (for they always 
demand time as an element) may the characteristic protraction of 
chemico-organic changes also be referred.” 
Granting, then, that microscopical evidence alone may not be 
quite satisfactory for settling the mode of origin of such prim- 
ordial living things as monads and bacteria, it becomes obvious 
that we must endeavour to throw light upon this evidence by 
other methods of investigation. Still it should also be kept 
steadily in mind that microscopical evidence is equally power- 
less to throw light upon those primordial collocations which 
initiate the formation of crystals. The problem concerning the 
primordial formation of crystals and living things is essentially 
similar in kind. Any difference in degree between our present 
knowledge on these two subjects must not blind us as to their 
essential similarity. Monads and bacteria are produced as con- 
stantly in solutions of colloidal matter as crystals are produced in 
solutions containing crystallisable matter. Crystallisable sub- 
stances are definite in composition, and give rise to definite 
statical aggregations ; whilst colloidal substances, much more 
complex and unstable, give rise on the contrary to dynamical 
aggregations. These dynamical aggregations, though they at 
first make their appearance in the form of monads and bacteria, 
are, by virtue of the properties of their constituent molecules, 
endowed with the potentiality of undergoing the most various 
changes, in accordance with the different sets of influences to 
which they are submitted. They are dynamical aggregates, in 
fact, in a condition of unstable equilibrium, and are capable 
of being diverted into new modes of current and reciprocal 
molecular activity in response to changes in their medium or 
environment. These differences between the products met with 
in solutions containing crystallisable and colloidal matter respec- 
tively, may, however, be due simply to the original difference 
in nature between such kinds of matter. Respecting the origin 
of the first visible forms which appear in either kind of solution, 
the evidence which we possess is precisely similar in nature. 
If such microscopical evidence does not enable us to get rid ot 
the doubt that the smallest visible specks of living matter may 
have originated from inzrsible “germs” of such organisms, 
neither does it any more enable us to dispense with the suppo- 
sition that the smallest visible crystals may have oziginated from 
pre-existing zzzvisib/e ‘*germs” of crystals. There is, in fact, so 
far as actual scientific evidence goes, almost as good reason for 
a belief in the universal distribution of invisible ‘‘ germs” of 
crystals, as there is for our belief in the universal distri- 
bution of invisible ‘‘germs” of monads and bacteria. The 
very existence of the one set of invisible ‘‘germs” is, in 
fact, just as hypothetical as the existence of the other. 
Monads and bacteria we do know; but concerning the exist- 
ence of invisible ‘‘ germs” of monads and bacteria we know just 
as little as we do concerning the existence of invisible ‘‘ germs” 
of crystals. a 
And yet almost all the difficulties in finally settling the ques- 
tion of the truth or falsity of the doctrines of ‘‘spontaneous gene- 
ration” are centered in this question as to the mode of origin of 
monads, bacteria, and such fungus-spores as similarly originate 
in homogeneous solutions in the form of the most minute specks of 
living matter.+ Given the existence of such primordial living 
particles, and we can easily watch changes taking place in aggre- 
gations of them, which lead to the production of much larger and 
altogether different organisms. We can then trace out with the mi- 
croscope various kinds of evolution—processes of so-called ‘‘spon- 
taneous generation,” in fact—the establishment of the reality of 
which is just as much in opposition to generally received biological 
notions, as is the supposition that the primordial units themselves 
are able to come into being de zovo after particular modes of 
* 
* Philosophical Transactions, 1862. Capitals and italics are employed as 
we give them in the memoir itself. 
t Such, for instance, is one of the modes of origin of Torna cells. 
NATURE 
UE 30, 1 870 
o 
collocation of colloidal molecules hitherto invisible. The amount 
of difference between such invisible organic molecule and the 
speck-like organism less than s>499” in diameter, which appears 
in the previously homogeneous solution, may be no more real or 
striking than is the difference between some of the visible monads 
or bacteria and the much larger and higher kinds of living 
things, whose mode of origin I am about to describe, and which 
may be seen to arise after particular sets of changes have taken 
place in aggregations of such monads and bacteria.- Of two things 
previously deemed alike improbable, the one which can come 
within the range of our vision may be shown to take place— 
the other being, unfortunately, beyond our ken, admits of no such 
proof. The unmistakeable upsetting of our preconceptions on 
the one subject should, however, make us cautious how, on theo- 
retical grounds, we pronounce that to be impossible in the case of 
organisms which we, nevertheless, believe to be possible and 
actual in the case of crystals: especially when, in these two 
sets of cases, the amount of actual evidence which we possess 
is almost equal and similar. 
Waiving, then, for the present the consideration of additional 
evidence as to the mode of origin of the primordial living 
particles, the monads and bacteria, and of the apparently simi- 
larly originating fungus-spores, I will describe some of the 
evolutional changes by which higher organisms may be seen to 
arise in a pellicle formed by an aggregation of the simpler kinds 
of living particles. 
I. 
The Mode of Origin of Unicellular Organisms and of Spores of 
Fungi in the “ proligerous pellicle” of organic solutions. 
°° ° oF 
What Burdach named the proligerous pellicle of organic solu- 
tions is made up of an aggregation of monads and bacteria in a 
transparent jelly-like stratum, on the surface of the fluid. It 
constitutes at first a thinscum-like layer, and although the monads 
and bacteria entering into its composition are motionless, M, 
Pouchet and -others were not warranted in assuming from this 
fact alone that they were dead. There is, indeed, good reason 
for believing to the contrary, since, as pointed out by Cohn, when 
any of these particles are set free from the broken edge of a 
pellicle they always resume their movements. Motion, therefore, 
may simply be prevented by the presence of the transparent jelly- 
like material in which they are imbedded, although the particles 
may be undoubtedly living. 
My observations on this subject have been principally carried 
on throughout the winter months ; and this is a time not favour-— 
able for the appearance of ciliated Infusoria in organic infusions. 
Hence it is, perhaps, that I have not been able to witness any 
of those changes in the pellicle which have been described by 
Pouchet, as resulting in the evolution of Paramvcia, Kolpode, 
and other ciliated Infusoria. The changes which I have ob- 
served, however, have been so indubitable in nature, have been 
seen so frequently, and have had such a close general resem- 
blance to those which have been described as leading to the 
evolution of Paramecia, that Iam quite disposed to believe in 
the correctness of the observations that have been made by 
Pouchet and others on this part of the subject. 
My own observations have been conducted principally on the 
pellicle of hay infusions, and one of the commonest processes of 
what may be termed sccondary organisation takes place in the 
following manner. In a pellicle which previously presented 
a uniform appearance, certain areas, altogether irregular in size 
and shape—though always presenting outlines bounded by 
curved lines—gradually make their appearance. ‘These are, at 
first, distinguishable from the general ground-work of the 
pellicle only by their somewhat lighter aspect. On careful 
microscopical examination with high powers, it may be seen that 
the boundary of such an area—measuring it may be as much, or 
more than 33,” in diameter—is pretty sharply defined from the 
surrounding unaltered granular stratum, The immediately con- 
tiguous granules of this are occasionally somewhat more tightly 
packed, though at other times no such change is observable. 
In either case the unaltered portion of the pellicle is quite different 
from the included lighter area, because in this an increase has, 
apparently, taken place in the amount of jelly-like material be- 
tween the granules, and, as well, there is a certain alteration in 
the refractive index, and occasionally in the size of the granules 
(monads and bacteria) themselves. The next change observable 
is, that the included area shows lines crossing it here and there, 
which at first tend to map it out into certain larger divisions, 
These intersecting lines gradually increase ia number, till at last 
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