Copyright
D. S. (David Samuel) Margoliouth.

The Popular science monthly (Volume 19) online

. (page 58 of 110)
Online LibraryD. S. (David Samuel) MargoliouthThe Popular science monthly (Volume 19) → online text (page 58 of 110)
Font size
QR-code for this ebook


ficial means of arresting the flow of flood ; and quite instantaneous in
insects. What prevents the blood from coagulating during life, or in
the blood-tubes, is unsettled. It can be prevented by salt.

The temperature of the blood depends upon the rapidity with



464 THE POPULAR SCIEXCE MONTHLY,

which the blood is oxidized ; and, within natural orders, it has a rela-
tion to the activity of the animal. For example, that of the swallow
is 111°, hen 109°, gull 100° ; among mammals, squirrel 105°, cat lOr,
dog 99°, man 98°. The animals called cold-blooded are only relatively
so, for fishes and reptiles have a temperature somewhat above that of
the water or air in which they live. Even the lower creatui'cs are
.slightly warmer than the surrounding medium.

The weight of the blood, which is always greater than that of
water, depends, of course, upon the amount of solid matter and the
abundance of the corpuscles. In man, the red corpuscles constitute
one third to a little less than one half the mass of the blood. The
blood of birds has the largest proportion ; and it appears that the tem-
perature bears a relation to the amount of solid matter.

The amount of blood is greater in warm-blooded animals ; and the
X>roportion of blood to the size of the body increases with the size.
The blood of man is by weight about one thirteenth the weight of the
body. The dog has blood equal to one fifteenth its body-weight ;
rabbit, one eighteenth ; cat, one twenty-first. The amount of blood in
the elephant and the whale has not been determined ; but the heart of
the whale is three feet in diameter.

The operation of ti'ansfusing the blood of a living animal into the
vessels of another, or of one that is dying, was known in ancient times,
and has been practiced at intervals for the last three hundred years.
Extravagant hopes concerning it were formerly entertained. It was
believed that diseases might be cured, impaired reason restored, old
age deferred, and even the dead returned to life. In late years the
eminent Brown-Sequard states that a dead dog was by this means
restored to life for twelve hours ; but the experiment has never been
confirmed, and doubtless the animal was not dead, as supposed. It is
also stated that a maniac was restored to reason by the blood of a calf.

In modern medical science, the transfusion of blood has become a
well-recognized operation for cases of exhaustion from simple loss of
blood. For this it is frequently practiced, and with success in the
majority of cases. For general weakness and disease it has sometimes
been used, but has not proved reliable.

The amoimt of blood used in transfusion is usually a very few
ounces, sometimes only one or two drachms — rarely ten or more
ounces ; a small quantity is safer. The blood of a different species of
animal is considered dangerous when used in large quantity. Venous
blood is preferred, and may or may not be defibrinated.

Pure milk has been successfully used instead of blood ; and even
artificial mixtures are employed. Richardson kept a monkey alive for
several weeks by a daily injection of an artificial blood.

The veins of the extremities are generally selected for the opera-
tion, they being less likely to admit air, which might be fatal by caus-
ing coagulation.



w



THE BLOOD AND ITS CIRCULATION. 465

From what has already been stated as the purpose of circulation,
we should not expect to find any circulation in those animals which
are destitute of a separate digestive cavity ; and in such we do not
discover a true blood-circulation. But it would appear that no animal
is entirely without the power of distributing its food to the parts of
the body. In the amoeba this is accomplished by the movements of
the protoplasmic body, whereby the portions which have enwrapped
and dissolved food-particles are blended with the less nourished parts.
The "contractile vesicles" of the amoeba may also have to do with
the distribution of nourishment, though they are usually regarded as
respiratory or excretory in function.

Next to this, in simplicity, is the prolongation of the digestive
cavity for the distribution of food. This is found in various animals
of different classes. The jelly-fish has a system of four canals, radi-
ating from the imperfect stomach, and uniting with a circular canal
at the margin of the body. We may regard this as the earliest devel-
opment of organs for conveying nutriment. A similar condition exists
in the anemone ; and spiders have prolongations of the stomach in
addition to their circulating organs.




\r^u-



^fe^ ^




Via. 6. Fia. 6.

CiRcnLATioN OF TOB SpiDKn Mygale Blondii. Fig. 5.— The stomach, with its rsDca and the
remainder of the alimentary canal, with the liver and Malpighian tubes. Fig. 6.— Heart and
arterial vessels.

True circulation is found only with a complete separation of the
digestive cavity from the visceral or general body cavity. In many
invertebrates there is simply a flux and reflux of nutritive fluid in
this visceral cavity, but no special circulating vessels. This is the
condition in the bryozoa, the lowest of mollusks, in the rotifera, and
in the larvJB of certain myriapods and insects. In these the fluid is
more the nature of chyle, and is called the chylaqueous fluid.

The " circulating system is gradually developed as an offset of the
visceral cavity." This is shown by the low ascidian mollusks, in

VOL. XIX. — 30



466



THE POPULAR SCIENCE MONTHLY.



which there is a sinus system prolonged from the visceral cavity, but
freely communicating with it. In this system the chylaqueous fluid
flows alternately in either direction, being propelled by a pump or
rudimental heart, which is only a muscular portion of one of these
sinuses. The same condition is found in some low crustaceans and
arachnids, and in the larvae of certain insects.

In former articles the sea-urchin has been noticed as the lowest

possessor of true teeth and stomach,
and we now have to award it the
added honor of the first distinct
heai't and blood-vessels.

The more highly organized in-
vertebrates have a muscular heart
and true arteries. But the blood
always enters the visceral cavity
before returning to the heart. In
other words, there is no closed cur-
rent in the invertebrates, the sys-
tem of circulating vessels being
in direct communication with the
body cavity. Regarding the cir-
culation of the lower invertebrates,
there, is still much uncertainty, as various sets of vessels are found in
different groups, the purpose of which is obscure, and their relation to
the blood-circulation a matter of investigation. The great variety in
the circulation of the many groups of invertebrates renders a detailed
description impossible. It will be consonant with the present purpose
to briefly describe only a few typical forms.

The typical system of the articulates is simply a segmented vessel




Fig. T— Diagram op SEA-UncmN. a. Anas;
6, Stomach ; c, Mouth ; c, Heart, which by
vascular rings encircles the alimentary
canal at d and /.




Fig. 8.— Diagram op Articulate Animal, a, Heart or Blood System ;
Nervous System.



Digestive System ; c.



lying lengthwise in the back of the animal. This dorsal tube, trunk,
or "heart," is open at both ends, and has openings along the sides,
guarded by valves. The chylaqueous fluid fills the body cavity,
bathing the heart and all the viscera. A puncture of the skin alone
allows the blood to issue. The walls of the tubular heart are mus-
cular and pulsatile. When the heart expands, the nutritive fluid is
drawn in at the hinder end and lateral apertures, and upon contrac-
tion it is forced forward and escapes at the forward end, being pre-
vented by valves from flowing backward or escaping laterally. The



TEE BLOOD AND ITS CIRCULATION.



467



fluid tinds its way backward through the lacunas or passages between
the tissues and viscera. The dorsal vessel prevents the stagnation of
the fluid.

In the myriapods the dorsal trunk has as many segments as there
are joints of the body. One of the millepeds has not less than one
hundred and sixty. Centipeds have generally twenty-one segments,
and besides the pair of valves for each joint there is given off a pair
of arteries. These unite to form a ventral tube. Insects have the
heart segmented only in the abdomen, and never more than eight
segments. An arterial prolongation of the trunk as a simple tube ex-
tends to the head.

As spiders and scorpions have localized breathing-sacs, they re-
quire a respiratory circulation. This
is secured, not by special tubes, but
by the passage of the blood, on its
return to the heart, through venous
sinuses or special passages between
the internal organs.

The best heart among articulates
is possessed by the crustaceans, the
largest, though not the highest, ani-
mals of the sub-kingdom. Crabs and
lobsters have a concentrated heart, a short, fleshy sac, with great pro-
pelling power, which sends the blood by several branching arteries to
the parts of the body. We now find a concentration of the power
which had been previously diffused in a long tube.




F1G.9.— Diagram OF Mollusk. a, Alimentary
Canal ; h, llcart ; w, «', n". Nervous
Ganglia.




Fio. 10— Crosp-sectiosal Diagram op a Fresh-watek Mussel. /. Ventricle ; y. Auri
Rectum ; |>, Pericardium ; A, t, Gills ; B, Foot ; A, A, Mantle or Skin.



As the moUusks are mostly so sluggish that their circulation has
little aid from the movements of the body, they require a more pow-



■WJ*.



468 THE POPULAR SCIENCE MONTHLY.

erful pump. In the higher mollusks the heart has generally two
cavities — an auricle for receiving the blood and a ventricle for pro-
pelling it. The bivalve mollusks have generally two auricles. In
the mollusks we discover a well-developed capillary system, but the
venous or return circulation is still partly lacunar. The heart of in-
vertebrates is always systemic — it forces the blood to the body, not to
the breathing-organs. But some of the cephalopod mollusks, the so-
called devil-fishes, have contractile cavities at the bases of the gills,
which act the part of a pulmonary heart, forcing the blood through
the breathing-organs on its way to the true heart. These accessory
hearts are called branchial hearts.

[To be continued.]



THE TEACHINGS OF MODERN SPECTROSCOPY.*

By Dk. ARTHUR SCHUSTER, F. R. S.

A SCIENCE, like a child, grows quickest in the first few years of
its existence ; and it is therefore not astonishing that, though
twenty years only have elapsed since Spectrum Analysis first entered
the world, we are able to speak to-day of a modern spectroscopy, with
higher and more ambitious aims, striving to obtain results which shall
surpass in importance any of those achieved by the old spectroscopy,
to the astonishment of the scientific world.

A few years ago the spectroscope was- a chemical instrument. It
was the sole object of the spectroscopist, to find out the nature of a
body by the examination of the light which that body sends out when
it is hot. The interest which the new discovery created in scientific
and unscientific circles was due to the apparent victory over space
which it implied. No matter whether a body is placed in our labora-
tory or a thousand miles away — at the distance of the sun or of the
farthest star — as long as it is luminous and sufficiently hot, it gives us
a safe and certain indication of the elements it is composed of.

To-day, we are no longer satisfied to know the chemical nature of
sun and stars ; we want to know their temperature, the pressure on
their surface ; we want to know whether they are moving away from
us or toward u§ ; and, still further, we want to find out, if possible,
what changes in their physical and chemical properties the elements
with which we are acquainted have undergone under the influence of
the altered conditions which must exist in the celestial bodies. Every
sun-spot, every solar prominence, is a study in which the unknown
quantities include not only the physical conditions of the solar surface,

* Address delivered at the Royal Institution of Great Britain, January 28, 1881.



THE TEACHINGS OF MODERN SPECTROSCOPY. 469

but also the possibly changed properties, under these conditions, of
our terrestrial elements. The spectroscope is rapidly becoming our
thermometer and pressure-gauge ; it has become a physical instru-
ment.

The application of the spectroscope to the investigation of the
nature of celestial bodies has always had a great fascination to the
scientific man as well as to the amateur ; for in stars and nebulas one
may hope to read the past and future of our own solar system. But it
is not of this application that I wish to speak to-day.

As there is no other instrument which can touch the conditions of
the most distant bodies of our universe, bodies so large that their size
surpasses our imagination, so is there no other instrument which equals
it in the information it can yield on the minute particles at the other
end of the scale, particles which in their turn are so small that we can
form no conception of their size or number. The range of the spec-
troscope includes both stars and atoms, and it is about these latter that
I wish to speak.

The idea that all matter is built up of atoms, which we can not
further divide by physical or chemical means, is an old one. As a
scientific hypothesis, however — that is, an hypothesis which shall not
only qualitatively, but also quantitatively, account for actual phe-
nomena — it has only been worked out in the last thirty years. The
development of molecular physics was contemporaneous with that of
spectroscopy, but the two sciences grew up independently. Those
who strove to advance the one paid little attention to the other, and
did not trouble to know which of their conclusions were in harmony,
which in discordance, with the results of the sister science. It is time,
I think, now that the- bearing of one branch of inquiry on the other
should be pointed out : where they are in agreement, their conclusions
will be strengthened, while new investigations will lead to more per-
fect truths where disagreement throws doubt on apparently well-estab-
lished principles.

What I have ventured to call modern spectroscopy is the union of
the old science with the modern ideas of the dynamical theory of
gases, and includes the application of the spectroscope to the experi-
mental investigation of molecular phenomena, which without it might
for ever remain matters of speculation or of calculation.

A body, then, is made up of a number of atoms. These are hardly
ever, perhaps never, found in isolation. Two or more of them are
bound together, and dq not part company as long as the physical state
of the body remains the same. Such an association of atoms is called
a molecule. When a body is in the state of a gas or vapor, each mole-
cule for the greater part of the time is unaffected by the other mole-
cules in its neighborhood, and* therefore behaves as if these were not
present. The gaseous state, then, is the one in which we can best
study these molecules. They move about among each other, and



•^ml^



470 TB£ POPULAR SCIEXCE MOXTHLY.

"within each molecule the atoms are in motion. Each atom, again,
has its own internal movement. But, if the world were made up of
atoms and molecules alone, we should never know of their existence ;
and, to explain the phenomena of the universe, we must recognize the
presence of a continuous universal medium penetrating all space and
all bodies. This medium, which we call the luminiferous ether, or
simply the ether, serves- to keep up the connection between atoms or
molecules. All communications from one atom to another, and from
one molecule to another, are made through this ether. The internal
motions of one atom are communicated to this medium, propagated
through space, until they reach another atom ; attraction, repulsion,
or some other manifestation takes place ; and, if you examine any of
the changes which you see constantly going on around you, and follow
it backward through its various stages, you will always find the motion
of atoms or molecules at the end of the chain.

The importance of studying the motion of molecules is therefore
clear ; and it is the special domain of the modern spectroscopy to in-
vestigate one kind of these motions.

When a tuning-fork or a bell is set in vibration, its motion is taken
up by the surrounding air, waves are set up, they spread and produce
the sensation of sound in our ears. Similarly, when an atom vibrates,
its motion is taken up by the ether, waves are set up, they spread, and
if of sufficient intensity produce the sensation of light in our eyes.
Both sound and light are wave-motions. A cursory glance at a wave
in water will lead you to distinguish its two most prominent attributes.
You notice at once that waves differ in height. So the waves both of
light and sound may differ in height, and to a difference in height cor-
responds a difference in the intensity of the souhd you hear or of the
light you see. The higher the wave the greater its energy, the louder
is the sound or the brighter is the light. But, in addition to a differ-
ence in height, you have noticed that in different waves the distance
from crest to crest may vary. The distance from crest to crest is the
length of the wave, and waves not only differ in height but also in
length. A difference in the length of a wave of soimd corresponds to
a difference in the pitch of the sound ; the longer a sound-wave is, the
lower is the tune you hear. In the case of light a difference in the
length of the wave corresponds to a difference in the color you see.
The longest waves which affect our eyes produce the sensation of red,
then follow orange, yellow, green, blue, and the shortest waves which
we ordinarily see seem violet. If a molecule vibrates, it generally
sends out a great number of waves which vary in length. These fall
together on our retina, and produce a compound sensation which does
not allow us to distinguish the elementary vibrations, which we want
to examine. A spectroscope is an instrument which separates the
waves of different lengths before they reach our retina ; the element-
ary vibrations, after having passed through a spectroscope, no longer



THE TEACHIXGS OF MODERN SPECTROSCOPY, 471

overlap, but produce their impressions side by side of each other, and
their examination and investigation is therefore rendered possible.

The elements of spectroscopy will be familiar to most of you, but
you will forgive me if I briefly allude to some points, which, though
well known, are of special importance in the considerations which I
wish to bring before you to-night,

When a body is sufficiently hot it becomes luminous, or, to speak
in scientific language, the vibrations which are capable of producing a
luminous sensation on our retina are increased in intensity as the tem-
perature is raised, until they produce such a sensation. By means of
a strong electric current I can in the electric lamp raise a piece of car-
bon to a high temperature. When looked at with the unaided eye it
seems whitehot, but, when I send the rays through a prism and pro-
ject them, as I do now, on a screen, you see a continuous band of light.
This fact we express by saying that the spectrum of the carbon poles
in the electric lamp is a continuous one. You see side by side the dif-
ferent colors known to you by the familiar but incorrect name of " the
rainbow-colors " ; and the experiment teaches you that the carbon
pole of the electric lamp sends out rays in which all wave-lengths
which produce a luminous sensation are represented-

But, if now I introduce into the electric arc a small piece of a vola-
tile metal, you see no longer a continuous band of light. The band is
broken up into different parts. Narrow bands or lines of different col-
ors are separated by a space sometimes black, sometimes slightly lumi-
nous. The metal has been converted into vapor by the great heat of
the electric current, and the vibrations of its molecules take place in
distinct periods, so that the waves emanating from it have certain
definite lengths. If the molecule could only send out one particular
kind of waves, I should in its spectrum only see one single line. We
know of no body which does so, though we know of several in which
the possible periods of vibration are comparatively few ; the spectrum
of these will, therefore, contain a few lines only. Thus we have two
different kinds of spectra, continuous spectra and line-spectra. But
there is a certain kind intermediate in appearance between these two.
The spectra of " fluted bands," as they are called, appear, when seen
in spectroscopes of small dispersive powers, as made up of bands,
which have a sharp boundary on one side and gradually fade away on
the other. When seen with more powerful instruments, each band
seems to be made up of a number of lines of nearly equal intensity,
which gradually come nearer and nearer together as the sharp edge is
approached. This sharp edge is generally only the place where the
lines are ruled so closely that we can no longer distinguish the indi-
vidual components. The edge is sometimes toward the red, some-
times toward the violet, end of the spectrum. Occasionally, however
the fluted bands do not show any sharp edge whatever, but are sim-
ply made up of a series of lines wliioli are, roughly speaking, equi-



472 THE POPULAR SCIENCE MONTHLY.

distant. No one who has seen a spectrum of fluted bands can ever fail
to distinguish it from the other types of spectra which I have described.

What, then, is the cause for the existence of these different types ?
The first editions of text-books in which our science was discussed
stated that a solid or liquid body gave a continuous spectrum, while a
gaseous body had a spectrum of lines ; the spectra of bands were not
mentioned. The more recent editions give a few exceptions to this
rule, and the editions which have not appeared yet, will — so I hope, at
least — tell you that the state of aggregation of a body does not directly
affect the nature of the spectrum. The important point is not whether
a body is solid, liquid, and gaseous, but how many atoms are bound
together in a molecule, and how they are bound together. This is one
of the teachings of modern spectroscopy. A molecule containing a
few atoms only gives a spectrum of lines. Increase the number of
atoms, and you will obtain a spectrum of fluted bands ; increase it
once more, and you will obtain a continuous spectrum. The scientific
evidence for the statements I have made is unimpeachable. In the
first place, I may examine spectra of bodies which I know to be com-
pound. Special precautions often are necessary to accomplish this
purpose, for too high a temperature would invariably break up the
compound molecule into its more elementary constituents. For some
bodies I may employ the low temperature of an ordinary Bunsen burner.
With others, a weak electric spark taken from their liquid solutions
will supply a sufficient quantity of luminous undecoraposed matter to
allow the light to be analyzed by a spectroscope of good power. The
spectrum of a compound body is never a line-spectrum. It is either a
spectrum of bands or a continuous spectrum. The spectra of the ox-
ides, chlorides, bromides, or iodides of the alkaline earths, for instance,
are spectra of fluted bands. All these bodies are known to contain
atoms of different kinds — the metallic atoms of calcium, barium, or
strontium, and the atoms of chlorine, bromine, iodine, or oxygen.

But to obtain these spectra of bands we need not necessarily have
recourse to molecules containing different kinds of atoms. Elementary
bodies show these spectra, and we must conclude therefore that the
dissimilarity of the atoms in the molecule has nothing to do with the
appearance of the fluted bands. Similarity in the spectrum must
necessarily be due to a similarity in the forces which bind the atoms
together, and this at once suggests that it is the compound nature of
the molecule which is the true cause of the bands, but that the mole-
cule need not be necessarily a compound of an atom with an atom of
different kind, for it may be a compound of an element with itself.
We -have ample proof that this is the true explanation of the different
types of spectra. I shall presently give you a few examples in support
of the view which is now nearly unanimously adopted by spectroscopists.



Online LibraryD. S. (David Samuel) MargoliouthThe Popular science monthly (Volume 19) → online text (page 58 of 110)