has recently reported, has adopted the view which I have explained in
this article as to the origin of feeble-mindedness. A large amount of
evidence was taken by the Commission from medical experts and others. A
certain number of the witnesses maintained the opinion that
feeble-mindedness arises from the action of deficiency of food, of
overcrowding, and possibly of drunkenness upon individuals of healthy
strain, whose offspring, as a consequence, exhibit feeble-mindedness.
Some naturalists, who have committed themselves to a pious belief in
what is vaguely called “the transmission of acquired characters,” think
themselves called upon to support this opinion, in consequence of a
notion that their belief would be rendered more reasonable than it is at
present were such an origin of feeble-mindedness demonstrated. Apart
from the fact that it is not demonstrated, it is difficult to see how,
supposing it were, such a causation could be considered as a
transmission of an acquired character. The ill-fed, drunken parent of a
feeble-minded child (when discovered and examined) is not found to have
“acquired” a condition of the brain agreeing with that of his or her
feeble-minded offspring, though sometimes such parent is found to have
been himself or herself born with a defective brain. No theory of
organic memory, of engrams, inscripts, or transfer of molecular
vibrations can enable us to present a plausible mechanical scheme of the
way in which the acquired general condition (restricting ourselves to
what is new and acquired) of an ill-fed parent can be definitely and
specifically re-embodied in his or her offspring, as the peculiar
structural condition of brain which is called “feeble-mindedness.” It
has not been shown, so far as I am aware, that privation in regard to
the food of a parental organism gives rise to new congenital qualities
in the reproductive germs which that organism throws off.
XXX
DEATH-RATES
The chief index or measure of the health of any locality is what is
called “the death-rate” of that locality. Although there are several
other important evidences as to the healthiness or unhealthiness of any
given area, the “death-rate” is the chief and most obvious indication of
the advantageous or disadvantageous action of the conditions of any
given city or other chosen area upon human life. Its records are more
easily kept with an approach to accuracy than are records of cases of
sickness not terminating in death. The cause of death has to be
certified in civilised communities by a medical man; the total number of
deaths in a year is given by the number of burial certificates. The
death-rate is stated at so many per thousand of the population per
annum. Thus, in a city of 5 million inhabitants,—that is to say, 5
thousand thousands—a record of eighty thousand deaths in the year gives
16 deaths for every thousand persons living. That is called “an annual
death-rate of 16.” The record for any single month may be stated (as it
is stated at intervals in the newspapers) “as at the rate of so many in
the thousand per annum,” by multiplying the actual monthly number per
thousand by 12. Thus, in the case of the city just cited, if the
death-rate were the same in every month of the year—namely, 16—it
would mean that 6500 persons died regularly every month. But we should
probably find that in some month or other as few as 5417 persons died.
That would be reported “as at the rate of” 13 per thousand per annum;
since, if every month gave only 5417 deaths, we should get 65,000 deaths
a year, which works out at 13 in the thousand in a population of 5
millions. In other months it might run as high as 19 or 20 (representing
over 8000 deaths a month), although, taking all the months together, the
deaths are at the rate of 16 in the thousand for the year.
The bald statement of the death-rate, of course, admits of much analysis
where proper records are kept. Thus the death-rate from different
diseases and groups of diseases can be stated, and the death-rate in
each group at different ages and for the two sexes can be given where
proper records are kept. In this country the records of population in
various areas and for the whole country, and of the deaths from various
causes, and at different ages, are collected and tabulated by the
Registrar-General and his officials. The annual reports issued by him
show what an amazing progress has been made in increasing the security
of life in our great cities within the last fifty years. Thus, in
London, the death-rate was, fifty years ago, 24 in the thousand. In 1906
it was only 15.1 in the thousand—it has gradually fallen, year by year,
so that now it is less than two-thirds of what it was half a century
ago. In Manchester and Liverpool it was about 26 twenty years ago, and
has fallen to 19 in Manchester and to a little over 20 in Liverpool. In
the same period the improvement has been (omitting fractions) from 19 to
14 in Bristol; from 20 to 16 in Birmingham; from 20 to 14 in Leicester.
This great diminution in the death-rate has been coincident with the
expenditure of public funds on the improvement of the water supply and
the sewage arrangements of those cities, as well as with the
enforcement of regulations to prevent overcrowding, and with the
demolition of the most insanitary houses. Rules as to the removal of
filth from the neighbourhood of dwelling-houses have been obeyed, and
sick persons suffering from infectious diseases have been removed from
dwelling-houses and conveyed to special hospitals. There is no doubt
that the diminished death-rate is due to the action thus taken, and more
will be done in the future to the same end. The proper provision of pure
milk (at a reasonable price) for the food of the youngest children, of
regular meals for older children, and the protection of adults from the
too frequent inducement to indulge in the use of distilled spirits, will
be taken in hand by the municipalities, and lead to a further diminution
in the death-rate.
We may, indeed, soon have to ask whether, in a population which has
become so much less subject to diminution by death than was formerly the
case, there is not too great an increase by birth—too great, that is to
say, for the existing means of employment and food-production. A most
serious, indeed, an alarming fact, has recently come to light in the
study of this question, namely, that the increase of the population is
due (as pointed out on p. 279) to the proportionately larger number of
births amongst the poorer, and even destitute, sections of the community
who have not the means of training and rearing their children
satisfactorily, and are themselves likely to transmit incapacity of one
kind and another to their offspring; whilst those who have valuable
hereditary qualities and are prosperous have—it is clearly
established—relatively few children—and, in fact, do not increase the
population. Whether this condition of things constitutes a real danger,
how it will ultimately work out if left alone, and how the difficulty is
to be met, are problems for statesmen which cannot be solved off-hand,
but require knowledge not only of the crude facts of statistics, but
also of the causes at work. Scientific knowledge—that is to say,
thorough and unassailable knowledge—of the laws of heredity, of
psychology, and of the natural history of human populations, are among
the essential qualifications for those who have to face and deal with
this difficult matter. And who is there who has this knowledge or is
even trying to obtain it? Not the State in this country or its
officials: for in every department of government (however capable some
of the subordinates may be) there is a determined opposition to and fear
of Science on the part of the political and highly paid chiefs—the
jealous fear due to complete and deadly ignorance.
XXXI
GOSSAMER
Fine as gossamer! Town-bred folks never see it, and do not believe in
its existence; they think it is a poetical figment, like “honey-dew.”
That, too, is nevertheless a real thing—a honey-like juice poured out
by the little plant-lice or aphides. Gossamer is a very real and a most
beautiful thing. You may see it on the hill-sides in fine October
weather, when the sun is bright but low enough to illuminate the
delicate threads and reveal the “veil of silk and silver thin” spread
over Nature’s loveliness. The innumerable threads glisten, and are so
fine that they shine with iridescent colours, as do the equally delicate
soap-bubbles fabricated by men and boys, and from the same cause. When
the eye gets accustomed to them and traces them—rippling and glimmering
over acres and acres of grass-land—one feels disconcerted, almost
awestruck, by the revelation of this vast network of threads. Sometimes
the gentle currents of air break them loose from the herbage, and they
float at a higher level and envelop the puzzled intruder in an almost
invisible entanglement of fairy lines. Sometimes they become felted
together in flakes and float or rest as incredibly delicate tissue,
woven by unseen mysterious agency.
[Illustration: FIG. 47.—A young spider (four times the natural length)
raising its body upwards, whilst the four silk threads (gossamer) spun
by it float in the air, and so draw out further liquid silk from the
spider. They increase in length to three or four yards, when they float
upwards, carrying the spider with them. (After McCook.)]
When the slopes of the new golf course at Wimbledon were covered last
autumn with gossamer, my friends were asking what was its origin, some
boldly asserting that it was impossible that such a vast acreage of
threads could be produced, as others maintained, by tiny unseen spiders!
Yet that is the true history of gossamer. Hundreds of thousands of
minute spiders, young, and of a small kind, are present in grass fields
in autumn, and throw out these marvellously fine threads from their
little bodies (Fig. 47). Those who at first sight doubt this origin of
gossamer are only in accordance with their forefathers. The French
peasants call it _fil de la Vierge_; old English writers held it to be
“dew evaporated.” A great discoverer and leader of science in his time,
Robert Hook, who was elected with Nehemiah Grew as secretary of the
Royal Society in 1677, and published a wonderful illustrated book called
_Micrographia_ (see p. 173), wrote of gossamer. He was so far from
recognising its true nature that he says: “It is not unlikely that those
great white clouds which appear all the summer time may be of the same
substance.” Yet it is now a simple and certain fact of observation that
the countless threads in question are the work of minute spiders!
The pretty name “gossamer” has puzzled the etymologists and led to some
far-fetched suggestions. That favoured by the authority of the great
Oxford dictionary of the English language is that it is a corruption of
“Go-summer,” because gossamer appears in autumn and is associated with
St. Martin’s summer. This is like saying that the word “cray-fish”
refers to fish that live in a “cray” or brook, instead of deriving it
from the French word _écrevisse_. The Germans call gossamer
_Sommerweben_. But the Latin word for cotton is _gossypium_; and there
is an Italian word, _gossampino_, which occurs in an English form,
_gossampine_, in the sixteenth century, and means a kind of silk or
cotton obtained from the fluffy hairs of a plant called bombax. We also
find “gossamer” spelt “gossamire” in English of that date; and it seems
to me most likely that an Italian word _gossamira_, signifying
“fairy-cotton” or “magic goose-down,” is the origin of our word.
[Illustration: FIG. 48.—View of the lower surface of the head and body
of a large Burmese spider, known as Liphistius, to show the spinnerets
(3 and 4), which are really reduced or rudimentary legs, and are in this
spider retained in their original position, instead of being pushed down
to the end of the body, as they are in all other spiders (see Fig. 49,
_spn_), I. to VI., the basal joints of the legs and palps of the
head-region; 1, the first abdominal segment; 2, the second; 3 and 4, the
legs of the third and fourth abdominal segments, which are the
spinnerets; 11, the eleventh abdominal segment—in front of it rudiments
of the segments 5 to 10 are seen; _an_, anus; _a_, _b_, inner and outer
lobes of the first pair of spinnerets.]
There are 500 different kinds of spider carefully described as occurring
in the British Islands, and about 2000 others from remoter regions.
Precisely which of them forms the “gossamer” of our meadows it is
difficult to say, as all have the habit of secreting a viscid fluid from
one or two pairs of projecting spinning knobs or stalks, which are seen
at the hinder end of the body (Figs. 48, 49, and 50). The viscid fluid
is poured out by a great number of minute tubes, and hardens at once
into a thread, which is wonderfully fine, yet strong. Different kinds of
spiders make use of these threads for different purposes, hence their
name “spinners.” Some make burrows in the ground and line them with a
felt of these threads, others enclose their eggs in a case formed by
winding them round the eggs, others form “snares” of the most marvellous
mechanical ingenuity with them, by which insects are entangled and are
then paralysed by the poisonous stab of the spider’s claws, and have
their juices sucked out of them at the spider’s leisure. The snares of
spiders are in some species merely irregular webs fastened and suspended
by threads, in other cases they are gracefully-modelled funnels or cups,
whilst a third kind, the disc-like webs made up of radiating and
circularly-disposed threads fixed in a geometrical pattern, excel—in
the mechanical precision of their workmanship and the masterly treatment
of engineering difficulties—the constructions of any other kind of
animal. It is amongst this kind of spiders that the formation by the
spinning knobs of threads or lines and their use in various ways is
most general and frequent. The smaller spiders expel the viscid thread,
drawing it out from their bodies by their own movement away from the
object to which it at first adhered. When it breaks loose from that
support it is carried upwards by air-currents and drawn out from the
spinners body to many yards’ length (Fig. 47). It then becomes a
“flying-line,” and the spider may sail away on it or run up it and
disappear. The celebrated story of the Indian juggler’s
performance—traditional and even solemnly attested by witnesses, but
failing to pass the test of photography—must have been suggested by
this common, yet wonderful, proceeding of small spiders. The juggler,
standing in an open place, surrounded by a ring of spectators, uncoils a
rope, 50 feet long, from his waist, and holding one end, throws the
other up into the air. The rope, without any support, remains stretched
and upright. A small boy now enters the ring and climbs up the rope,
draws it up after him, and disappears with it in the upper air! That is
an illusion, but it is precisely what thousands of small spiders are
continually doing. A big spider—the well-grown female of the common
garden spider, for instance, cannot do this—her thread is not strong
enough, and her weight is too great. But the male of the same species,
who is much smaller, fortunately for him, can safely run on a hanging
line—and thus can rapidly escape from the side of his mistress, who,
after receiving his caresses, has an unpleasant habit of seizing,
killing, and sucking the blood of the adventurous male, should he linger
longer in her company, and fail in the agility and rapidity of his exit.
[Illustration: FIG. 49.—Section through the body of a spider to show
the spinning organs. _h_, heart connected by four big veins with _b_,
the lung-bosks or air-gills; _f_, genital lid; _ov_, ovary; _a_, the
anus; _spn_, the three pairs of spinnerets or spinning warts; _c_, _e_,
and _d_, the three kinds of glands producing liquid silk, viz.,
cylindrical, tree-form, and pyriform. These are one thousand in number
in the common garden spider, and each has its separate spout or spigot
standing up on one of the spinnerets (see next figure).]
[Illustration: FIG. 50.—One of the two middle spinnerets of the common
garden spider (_Epeira diadema_), to show the three kinds of spouts or
spigots (one thousand in all) corresponding to the three kinds of
silk-glands. Each kind of “spigot” pours out a different kind and size
of thread. _sp.c_, one of the big spigots of the cylindrical glands;
_sp.t_, middle-sized spigots belonging to the tree-form glands; _ss_ and
_s.ss_, the small-sized spigots of the very numerous pyriform glands.]
The threads of the garden spider (the _Porte-croix_ of the French,
white-cross spider, _Epeira diadema_, Fig. 51) are fixed by astronomers
in their telescopes for the purpose of giving fine lines in the field of
view, by which the relative positions of stars may be accurately
measured. For a century astronomers desired to make use of such lines of
the greatest possible fineness, and procured at first silver wire drawn
out to the extreme limit of tenuity attainable with that metal. They
also tried hairs (1/500th of an inch thick) and threads of a silk-worm’s
cocoon, which are split into two component threads each only 1/2000th of
an inch thick. But in 1820 an English instrument maker named Troughton
introduced the spider’s line. This can be readily obtained three or four
times smaller in breadth than the silk-worm’s thread, and has also
advantages in its strength and freedom from twist. In order to obtain
the thread, the spider is carefully fixed on a miniature “rack,” and the
thread, which at the moment of issue from the body is a viscid liquid,
is made to adhere to a winder, by turning which the desired length of
firm but elastic thread can be procured. It has been proposed to use
spiders’ silk in manufactures as a substitute for silk-worms’ silk, and
pioneers have woven gloves, stockings, and other articles from it. It
appears that there are species of spider in other parts of the world
whose thread is coarser and more suitable for this purpose than that of
any of our British spiders. But it is estimated that the expense in
feeding the spiders—which require insect food—would make the thread
obtained from them far too costly to compete with silk-worm silk.
[Illustration: FIG. 51.—The common garden spider, more correctly called
the white cross spider (_Epeira diadema_): a female drawn a little
(one-fifth) larger than life.]
A number of different kinds of the lower animals besides spiders have
the power of producing threads. The caterpillars of some moths are
especially noted for this, since their thread is familiar to us all as
“silk.” It is secreted as a viscid fluid by a pair of tubes opening at
the mouth, and hardens on escape. Even some marine creatures—the
mussels—produce threads, in this case from a gland or sac in the
muscular foot, by means of which they fix themselves to rocks. A very
big mussel—the _Pinna_—called _Capo lungo_ by the Mediterranean
fishermen and _Capy longy_ at Plymouth, where they are also found,
produces a sufficient quantity of fine horny threads to be used in
weaving, and gloves have been made at Genoa from the shell-fish silk.
The threads produced by the hardening of the tenacious fluid exuded by
these various animals were probably simply protective in origin. The
curious caterpillar-like creature _Peripatus_ spits out a viscid fluid
when it is disturbed, which hardens into threads, and hopelessly
entangles any small enemy which may venture to attack it. Threads of a
poisonous nature are thrown out by jelly-fishes, polyps, and sea
anemones, and serve them both as defence and as means of paralysing and
capturing prey. A later stage in the use of such threads is their
“felting” to form a case or tube (as in the sea anemone called
_Cerianthus_), and so their application has gradually developed to the
formation of egg-cases, snares, and the wonderful web of the geometric
spider, and the countless “flying-lines” of smaller spiders, which make
up the mysterious thing we call “gossamer.”
As to the limits of the tenuity of the threads of gossamer there are no
direct observations. Probably they are often as fine as the 1/16,000th
or 1/20,000th of an inch in diameter. The condensation of a very minute
quantity of moisture on gossamer threads and spiders’ webs no doubt
helps to make them more readily visible to us in October weather than
they are in full summer, when such moisture would not condense except in
early morning or at sunset. It seems strange that man should have been
unable to produce a thread so fine as that of the spider, but this
reproach has now been removed. Spun glass is easily obtained 1/1000th of
a inch in diameter; but Mr. C. V. Boys, F.R.S., has, by fusing quartz
(rock-crystal) by the oxy-hydrogen flame, and drawing it out by means of
a small arrow (a straw), discharged from a bow—the near end of the
arrow being adherent to a fused droplet of quartz which is held
fast—produced threads of great strength and of extraordinary tenuity.
The fineness can be regulated by the rapidity with which the drawing is
effected. The threads are prepared (for use in suspending swinging bars
in delicate measurements of force) of a thickness of 1/10,000th of an
inch. Some have been made so fine as to be not only invisible to the
naked eye, but to be only vaguely indicated by the highest powers of the
microscope. They are estimated to be only one-millionth of an inch in
diameter. It is difficult to form any mental picture or conception of
these finest quartz threads spun by Mr. Boys. But the following fact
helps us to realise how delicate they are. A grain of sand just visible
to the eye—that is to say, 1/100th an inch long, the same in breadth,
and the same in height—would make twenty miles of such thread.
XXXII
THE JUMPING BEAN
One way of thinking of the six hundred thousand kinds or species of
insects—those tiny, ubiquitous fellow-creatures of ours which inhabit
nearly every corner and cranny of the earth’s surface—is to associate
them with the plants upon which, either for food or protection, the
greater number of them are dependent. This makes them appear less
overwhelming in their astonishing and, at first sight, meaningless
variety, than when one calls them to mind pinned out in long lines in
innumerable drawers and cases, or assorted, like with like, in the
wonderfully accurate and interminable pictures of them produced by those
patient benefactors of mankind the systematic entomologists. Every plant
of any size has a number of insects associated with it, living more or
less completely on its substance, or making its home in some part of the
plant. Some trees are known to have more than a hundred and fifty kinds
or species of insects thus dependent on them, those which are vegetarian
serving in their turn as food to a variety of carnivorous insects.
The ways in which insects are associated with plants may be briefly
stated. It must be remembered that often, though not always, one
particular species of plant, and that only, is capable of serving the
needs of a given species of insect. Thus, the leaves of a given plant
are the necessary food of the grubs of one or more insects which bite
their food; its internal juices serve others which suck; its roots
others; its nectar in the flower others, which in return serve the plant
by carrying away its pollen and fertilising the other plants of the same
species which they visit. Protection is sought and obtained from the
same plant by insects which burrow in its leaves, or roll them up, or
cut them into slices and carry them away, or hide in its bark, or in the
flowers, or in other parts—or burrow for food and shelter into its
wood. Others lay their eggs in the soft buds, producing or not producing
according to their kind distorted growths, known as “galls” (one plant
is known to have as many as thirty species of gall-flies which make use
of it). Other insects lay their eggs in the flower-buds and immature
fruits, or place them on the plant so that the young grubs, when
hatched, can at once eat into those soft parts. Others bore into the
wood or into hard or fleshy fruits expressly to lay their eggs, or into
the ripe seeds. Certain ants live in chambers specially provided by the
woody parts of the plant for them, and benefit both themselves and the
plant by devouring other insects which seek the plant in order to devour
it. In a museum of natural history there should be exhibited at least
one plant with specimens and enlarged models of all the insects which
depend upon it for food, protection, or nursery, and with accompanying
illustrations of the way in which those purposes are served.