takes place under ordinary circumstances. The action of
respiration exposes the blood to the air, and, by mutual
diffusion, the two actions of oxygenating the blood and freeing it
of carbonic acid are accomplished by the same act, thus resembling
the chemical processes of nature known as endosmosis and exos-
mosis. The process as applied to the fluids and gases of the
body is termed osmosis. The action of gaseous interchange
involved with the process of respiration is owing to reflex nervous
action and not dependent on the will, as the same process goes
on in sleep and in other unconscious states. The lungs themselves
are almost passive in the process. From every 100 cubic centi-
metres of arterial blood rather more than 20 cubic centimetres of
oxygen can be removed by the air pump . Nearly all of this oxygen
is chemically combined with haemoglobin. The amount, though,
in actual solution is small, being o'7 centimetre for every 100
centimetres. Hemoglobin owes its value as a respiratory pigment
to these principal facts : Firstly, it can unite with a large quantity
of oxygen ; in fact it can carry about thirty times as much to the
THE CIRCULATORY SYSTEM 91
tissues as plasma would under the same circumstances. Secondly,
the interaction between haemoglobin and oxygen is a reversible
one: the two unite in the lungs where the pressure is high, but
when oxygen is absent or at a low pressure, as in the tissues, the
haemoglobin parts with its store of oxygen.
If blood is divided into its two separate parts plasma and
corpuscles it will be found that both yield carbonic acid, but
the yield from the plasma is the greater.
One hundred volumes of venous blood contains about 46
volumes of carbonic acid gas. But, although arterial blood contains
20 per cent, of oxygen gas, and venous blood contains 46 per cent,
of carbonic acid gas, yet this by no means represents the actual
amount of these gases inspired or respired at each movement of
breathing. These gases are always present in the blood together
at the same time, and only a small proportion is interchanged.
Arterial blood contains :
Oxygen, 20 per cent.
Carbonic acid gas, 40 per cent.
Nitrogen, 2 per cent.
Venous blood contains :
Oxygen, 8 to 12 per cent.
Carbonic acid gas, 46 to 50 per cent.
Nitrogen, i to 2 per cent.
It will be noticed that the amount of nitrogen in the blood
is small in amount. It has no physiological significance, and
is nearly the same in both varieties of blood. The important
distinction between arterial and venous blood is in .the other two
gases, and, as the table shows, on the average every 100 cubic
centimetres of venous blood which passes through the lungs
gains 8 cubic centimetres of oxygen and loses 6 of carbonic
acid gas.
Osmosis or Diffusion in Gaseous Interchange.
The principle of the gaseous interchange which occurs in the
blood while passing through the lungs is called diffusion or osmosis.
When applied to gases it means the passing of one gas into the
space occupied by another. When applied to liquids it means
that when two liquids that are capable of mixing are put into
contact with a thin separating medium of parchment between
them they gradually diffuse one into the other, notwithstanding
92 OPERATIVE DENTAL SURGERY
the action of gravity. Thus, if a vessel containing a solution of
common salt be carefully placed with its mouth covered in a
vessel containing water, the water being sufficiently deep to cover
the vessel of salt and water, and if the cover be removed from
that vessel, in time the salt and water solution will diffuse out
into the larger vessel, and the water into the smaller vessel, until
both fluids are of equal density. With gaseous interchange
in the lungs we have the same principle of a thin membrane
separating two chemicals, but it is gaseous with a liquid vehicle.
There are, accompanying this form of osmosis or diffusion, many
complicated factors which are conformable to physical, physio-
logical, anatomical, and chemical laws, which are thoroughly
understood by authorities on the blood.
The Control of the Capacity of Arterioles by Vasomotor Nerves.
Another characteristic of the blood circulation, and which is
of paramount importance, is the control of its flow by the condi-
tion of the bloodvessels as to their carrying capacity under various
conditions of the general system or local parts. The carrying
capacity of the arteries and veins is controlled by what is called
the vascular nervous system.
Arteries are supplied with nerves which are derived from the
sympathetic nervous system. They form intricate branching
centres, called plexuses, upon the surfaces of the larger trunks, and
run along the smaller arteries as single filaments or bundles of
filaments, which twist around the vessel and unite with each other
in a plexiform or network manner. The branches derived from
these plexuses penetrate the external coat of arteries and are
distributed principally to the muscular tissue of the middle coat,
and thus regulate, by causing the contraction and relaxation of
this tissue, the amount of blood sent to any part.
Veins are also supplied with nerves, but in much less abundance.
The vascular nervous system is termed the vasomotor system
and consists of the vasomotor centre, which is situated in the
base of the brain, called the medulla, also of certain subsidiary
vasomotor centres in the spinal cord, and of vasomotor nerves,
which are of two kinds :
1. Vaso-constrictor nerves, which cause constriction or con-
traction of bloodvessels.
2. Vaso-dilator nerves, which cause dilation.
THE CIRCULATORY SYSTEM 93
Peripheral Resistance in the Arterioles of Great Importance.
The nerves exert their most important action in the vessels
which contain relatively the greatest amount of muscular tissue,
viz., the smaller arteries or arterioles. Under ordinary circum-
stances the arterioles are maintained in a state of moderate or
tonic contraction, and this constitutes the normal peripheral
resistance, the use of which is to keep up the arterial pressure,
and which must be high enough to force the blood through the
capillaries and veins in a continuous stream back to the heart.
Another function which is served by this muscular tissue is to
regulate the amount of blood which flows through the capillaries
of any organ, locally, in proportion to its needs. The vasomotor
centre can be excited directly by electric induction currents ; the
result is an increase of arterial blood-pressure, owing to an increase
of the contraction of the peripheral arterioles. It can also be
excited by the action of poisons in the blood which circulate
through it. Strophanthus or digitalis causes a marked rise of
general arterial pressure, due to the constriction of the peripheral
vessels brought about by impulses from the centre. It is also
excited by the condition of venous blood, as in asphyxia. The
rise of blood-pressure which occurs during the first part of
asphyxia is due to the constriction of peripheral vessels, and the
fall of pressure during the last stage of asphyxia is largely due to
heart failure.
The vasomotor nervous system is influenced to some extent
by conditions of the cerebrum, some emotions, such as fear,
causing pallor by vaso-constriction, and others causing blushing
by vaso-dilatation. It is almost impossible to over-estimate the
importance of the study of vasomotor phenomena as a means of
explaining certain pathological conditions . In certain conditions,
for instance, which lead to angina pectoris, the pain in the heart
is, in part, due to its being unable to overcome an immense peri-
pheral resistance, and the condition is relieved by the administra-
tion of such drugs as amyl-nitrite or nitro-glycerine, which relax
the vessels and cause universal blushing.
Asphyxia and its Causes.
The condition of asphyxia is a most important one to be taken
into consideration by every dental practitioner when referring
to the vasomotor nervous system.
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94 OPERATIVE DENTAL SURGERY
Asphyxia may be produced in various ways :
1. By the prevention of the due entry of oxygen into the blood,
either by direct obstruction of the trachea or other parts
of the respiratory passage.
2. By introducing, instead of ordinary air, a gas devoid of
oxygen.
3. By interference with the due interchange of gases between
the air and the blood.
Stages of Asphyxia.
The symptoms of asphyxia may be roughly divided into three
stages :
1. Exaggerated breathing.
2. Convulsions.
3. Exhaustion.
In the first stage breathing becomes more rapid and deeper
than usual, inspiration at first being especially exaggerated and
prolonged. The muscles of extraordinary respiration are called
into action, and the effort to respire is laboured and painful.
This is soon followed by a similar increase in the expiratory efforts,
which become excessively prolonged, being aided by all the
muscles of extraordinary expiration. During this stage, which
lasts a varying time from a minute upwards according as the
deprivation of oxygen is sudden or gradual, the lips become blue,
eyes are prominent, and the expression intensely anxious. The
prolonged respirations are accompanied by a distinctly audible
sound, and the muscles attached to the chest stand out as distinct
cords. This stage includes the two conditions hyperpncea, or
excessive breathing, and dyspnoea, or difficult breathing, which
follows later. It is due to the increasingly powerful stimulation
of the respiratory nervous centre by the increasingly venous
blood.
In the second stage, which is not marked by any distinct line
of demarcation from the first, the violent expiratory efforts
become convulsive, and then give way to general convulsions,
which arise from the further stimulation of the centres in the
brain and spinal cord by the venous blood. Spasms of the
muscles of the body occur in general, and not of the respiratory
muscles only. The convulsive stage is a short one, and lasts less
than a minute.
THE CIRCULATORY SYSTEM 95
The third stage is that of exhaustion. In it the respirations
all but cease, the convulsive spasms give way to flaccidity of the
muscles, there is insensibility, the conjunctiva of the eyes are
insensitive, and the pupils are widely dilated. Every now and
then a prolonged sighing inspiration takes place, at longer and
longer intervals, until breathing ceases altogether, and death
ensues. During this stage the pulse is scarcely to be felt, but
the heart may beat for some seconds after the respiration has
stopped. The condition is due to the gradual paralysis of the
nerve centres by the prolonged action of the venous blood. This
stage may last three minutes and upwards. After death from
asphyxia it is found in the great majority of cases that the right
side of the heart, the pulmonary arteries, and the systemic veins
are gorged with dark, almost black, blood, and the left side of
the heart, the pulmonary veins, and the systemic arteries, are
empty. The explanation of these appearances is thus summar-
ized. When oxygenation ceases, venous blood at first passes
freely through the lungs to the left heart, and so to the great
arteries. Owing to the stimulation of the vasomotor centres
by the venous blood the arterioles become constricted through
the vaso-constrictor nerves. The arterial blood therefore rises
and the left side of the heart becomes distended. The highly
venous blood passes through the arterioles, and, favoured by the
laboured respiratory movements, arrives at the right side of the
heart, which it fills and distends. The right side of the heart
becomes feebler at the same time, because of its overloaded con-
dition, and therefore unable to effectively discharge its blood
through the pulmonary circuit in the lungs. Simultaneously the
left ventricle is also becoming weakened, and therefore the suction
action diminishes. In this way the blood is dammed back in the
right heart and veins, and the left side of the heart, therefore, gets
into the empty condition in which it is found after death.
In the first stages of asphyxia the arterial pressure rises above
the normal; this is due to the constriction of the arterioles. The
fall of pressure in the last stage is mainly due to heart failure.
CHAPTER VII
THE CIRCULATORY SYSTEM (Continued)
THE IMMUNITY OF THE BLOOD AND ITS COAGULATIVE PROPERTIES,
WITH RELATION TO ASEPSIS AND HAEMORRHAGE.
THE consideration of the remaining two great divisions of the
vital functions of the blood is of no less importance to the dental
operator than the preceding chapter, but we would, however, lay
stress on the points before us as being the goal to which we have
deliberately led our readers in the foregoing description of the
circulation of the blood. The operations upon the teeth and
the tissues surrounding them, when skilfully carried out, should
maintain at least the normal degree of health which obtained
when the patient presented himself. The object of the dental
operator in all operations is to bring all diseased conditions up to
the patient's normal state of health. We would also remark
that no operator is justified in making the degree of inflammation
worse than when he first found it, even if he does not succeed in
making it better, but he must so master his work that the normal
degree of health is reached by his selection of operative methods
and suitable medical treatment.
Most operators take it as a matter of course that when they
extract a tooth the fearful wound will take care of itself, and the
same view of the operation is extended to thousands of teeth
extracted, and yet they are enormously surprised, and in some
cases mystified, by the fact of a case here and there causing
some anxiety both to themselves and their patients on account
of the tardiness of the socket to heal up. There may be consider-
able sloughing, and in some cases a decided disinclination to
heal up, apart from asepsis. To take a rational estimate of these
cases by comparison with the cases that heal up without any
trouble at all we ought to reverse them, and the surprise and
wonder should be expressed by the question, Why do these
straightforward cases heal up so nicely ? The operator should at
all times regard all extraction operations as being on a level with
96
THE CIRCULATORY SYSTEM 97
root treatment, which would lead him to be ready for reverse
developments and deal with them accordingly. The two opera-
tions of extraction and root treatment, though usually regarded
as being wide apart in the degree of skill involved, are identical
in their principles of maintaining or reaching the normal degree
of health of the socket tissues. To put it clearly, we will assume
that a patient presents himself with an abscessed tooth before
two operators. One decides to extract the tooth, the other one
undertakes to cure the abscess and save the tooth. The principle
that is identical in the two operative methods is that the health
of the tissues must be secured in either case, and in each method
the abscess is dealt with in order to rid the socket of septic
trouble. But the operator who extracts the tooth has much
the easier task, because in removing the tooth he can at once
reach the abscess, which he sometimes is apt to leave to itself
with serious consequences. The second operator, who decides
to treat the abscess in order to cure it, voluntarily undertakes
all the risks because he realizes the factors that will help him,
although his work may be tedious and difficult, yet he is con-
fident of a ready response of the tissues to his treatment.
The Factors underlying all Dental Operations.
What, then, are the factors that help the dental operator in
his work ? The definite answer to this vital question is :
1. The resistance of the blood to bacterial invasion, indicated
by the term immunity.
2. Coagulation of the blood, in order that the normal quantity
in circulation shall not be seriously reduced through
bleeding and pending repair of the bloodvessels.
Immunity of the blood is its power of resisting the development
of infections, or morbid processes, in the body. This property
is exercised by the presence of various chemical constituents
such as agglutinins, lysins, opsonins, and antitoxins. The study
of these substances can only be undertaken in suitable labora-
tories where the exacting precision of analysis may be verified
and recorded. There are definite methods of investigation which
produce tangible evidence of the existence of the factors that
are involved in the resistance of the blood to the activities
of bacteria. The instruments used include elaborate scientific
equipment, and such instruments as the microscope and its
7
98 OPERATIVE DENTAL SURGERY
never-ending adjustments for magnification and illumination,
the spectroscope, with which the shades and colours of chemical
substances can be detected and measured, and also elaborate
electrical apparatus. So that there is no lack of evidence that
the proofs of recognition of the substances examined are beyond
doubt when verified and corroborated by several experts in these
subjects.
Natural immunity of the blood, organs, and tissues of the body
is carried out by their own inherent chemical constituents.
Their action in combating particular bacteria may be increased
by the inoculation of chemical substances, called antitoxins.
They are employed in suitable strengths, and under proper con-
ditions of administration, whereby their chemical and bacteri-
ological activities are maintained for a long period of time.
It can be acquired also by the chemical products of certain
diseases whereby the blood is immune against a repeated attack
of that disease, such as smallpox, or vaccination for the preven-
tion of that disease, which has the same effect. This last method
of inoculating anti-toxin is termed artificial.
It must be understood that the degree of immunity varies
considerably in consequence of various factors. The importance
of the discoveries regarding immunity becomes more valuable to
us in proportion as we realize that the blood contains within itself
the means whereby disease can be combated. The life of an
organism is in its blood; the blood is the life, and keeps it in a
positive condition. Any interference with its normal condition of
health gives rise to inflammation, so that it may be regarded as
the evidence of the action of the blood to cast out the germs of
threatened disease. It is in reality a combat between the police-
men contained in the blood and the invading bacterial enemy.
In this way the body is protected by chemical defences against
injury and disease.
The acid of the gastric juice in the stomach is a great protection
against harmful bacteria being introduced with food. The
acidity of urine has a marked effect upon bacterial growth within
that secretion.
The leucocytes, or white corpuscles, called also phagocytes,
destroy bacteria by feeding upon them (see Chapter VI.). Also
the fluid part of the blood is often antagonistic to bacterial life.
This fact was first discovered when bacteriologists experimented
with blood serum as being a suitable medium in which to grow
THE CIRCULATORY SYSTEM 99
or cultivate bacteria. It was thought quite probable that it
would be a natural soil for it, but it was found in some instances
to have just the opposite effect.
The bactericidal powers of the blood, however, are destroyed
by heating it for some time to 55 C. The chemical substances
contained in the serum are called bacteriolysins.
Besides the bactericidal powers of the blood serum there is also
present its globulicidal power. This means that the blood serum
of one animal has the power of dissolving the red corpuscles of
another species. If the serum of one animal is injected into the
blood-stream of another species the result is a destruction of its
red corpuscles, which may be so excessive as to lead to the passing
of the liberated haemoglobin into the urine (called hsemoglo-
binuria).
The substances in the serum possessing this property are called
haemolysins, and although there is some doubt whether bacterio-
lysins and haemolysins are identical, yet they are very closely
related substances.
Normal blood possesses a certain quantity of substances which
are inimical to the life of our bacterial foes, but when a person
gets run down it is common knowledge that he is then more liable
to catch anything. This coincides with a diminution in the bac-
tericidal power of his blood. But even a healthy person has not
an unlimited supply of bacteriolysui, and if the bacteria are
sufficiently numerous he will fall a victim to the disease which
they produce. Here, however, comes in the remarkable part of
the defence. In the struggle he will produce more and more
bacteriolysin, and if he gets well it means that the bacteria are
finally vanquished, and his blood remains rich in the particular
bacteriolysin he has produced, and so will render him immune
for a tune to further attacks from that particular species of
bacterium. Each bacterium attacked in this way seems to
cause the development of a specific antibody.
The blood has the means of combating our bacterial enemies
in various ways. In some cases they are rendered immobile by
agglutinins, in other cases they are killed by bacteriolysins. In
other instances their toxins are neutralized by antitoxins, and
in others, again, they are directly devoured by the phagocytes.
Metchnikoff 's view, which is shared by many eminent bacteriolo-
gists, is that phagocytosis, or the devouring function of the phago-
cytes or leucocytes, is the supreme method, and the others are
loo OPERATIVE DENTAL SURGERY
auxiliary. The immunity of the blood is therefore a vital factor
to the dental operator in the healing up of wounds and sockets
after extractions, and this should be taken into serious considera-
tion in dealing with weak patients, and also with mouths that
present an extremely unhealthy appearance. In injecting alka-
loids such as cocaine, etc., it must be borne in mind that they are
protoplasmic poisons, and if the parts are already inflamed and
diseased it cannot be expected that the injection of a tissue
poison is going to help the healing of them. But providing the
operator is aware of the condition of his patient he can, as a rule,
help the case materially by using suitable antiseptic mouth-
washes and bringing the patient back for treatment until the
parts are healthy. The wonderful activity, however, of the
periosteum may be counted upon, but as it is so delicate it must
be helped by mild antiseptic and prophylactic treatment ; in other
words, get that organ healthy and it will then attend to the
healthy repair of the bone, which is the main consideration in
dental operations. The medical man can render valuable aid
by administering suitable medicines and treatment systemically
in bad cases.
The Basic Principles of the Process of Coagulation.
The third great division of the vital functions of the blood
comes under the term ' ' coagulation . ' ' This quality of the blood is
equally of importance to the dental operator as the two we have
already described. This is another instance where the body has
a means of defence. In this case it is a protection against loss
of blood, with its dire and calamitous consequences. There are
some persons (fortunately few) who suffer from what is called
" haemorrhagic diathesis," which means that they bleed freely
and profusely from the slightest scratch or cut, and their blood
is so peculiar that there is the greatest difficulty in stopping its
flow. This disease is fortunately of not very common occurrence.
Thus patients and parents of children with this tendency should
always inform the dentist of this fact if they are aware of it, in
order that, as far as possible, it can be dealt with previous to the
operation, so that the serious loss of blood may be prevented
when the operation does take place. But there are very rare
cases where no treatment whatever will be available. Such cases,
when known beforehand, should be placed in the hands of a
THE CIRCULATORY SYSTEM 101
medical man for treatment before and after the operation. But
the treatment of haemorrhage after the extraction of teeth can
usually be made successful if the principles of the coagulation
of the blood are understood. It is not our intention in this
chapter to deal with the practical treatment of haemorrhage, but
we will do so in the proper place in a future chapter.
When blood is drawn and allowed to stand it emits a " halitus "