CONDITIONS WHICH INTERFERE WITH REPAIR
SURGICAL BACTERIOLOGY
Want of rest--Irritation--Unhealthy tissues--Pathogenic bacteria.
SURGICAL BACTERIOLOGY--General characters of
bacteria--Classification of bacteria--Conditions of bacterial
life--Pathogenic powers of bacteria--Results of bacterial
growth--Death of bacteria--Immunity--Antitoxic sera--Identification
of bacteria--Pyogenic bacteria.
In the management of wounds and other surgical conditions it is
necessary to eliminate various extraneous influences which tend to delay
or arrest the natural process of repair.
Of these, one of the most important is undue movement of the affected
part. "The first and great requisite for the restoration of injured
parts is _rest_," said John Hunter; and physiological and mechanical
rest as the chief of natural therapeutic agents was the theme of John
Hilton's classical work--_Rest and Pain_. In this connection it must be
understood that "rest" implies more than the mere state of physical
repose: all physiological as well as mechanical function must be
prevented as far as is possible. For instance, the constituent bones of
a joint affected with tuberculosis must be controlled by splints or
other appliances so that no movement can take place between them, and
the limb may not be used for any purpose; physiological rest may be
secured to an inflamed colon by making an artificial anus in the cæcum;
the activity of a diseased kidney may be diminished by regulating the
quantity and quality of the fluids taken by the patient.
Another source of interference with repair in wounds is _irritation_,
either by mechanical agents such as rough, unsuitable dressings,
bandages, or ill-fitting splints; or by chemical agents in the form of
strong lotions or other applications.
An _unhealthy or devitalised condition of the patient's tissues_ also
hinders the reparative process. Bruised or lacerated skin heals less
kindly than skin cut with a smooth, sharp instrument; and persistent
venous congestion of a part, such as occurs, for example, in the leg
when the veins are varicose, by preventing the access of healthy blood,
tends to delay the healing of open wounds. The existence of grave
constitutional disease, such as Bright's disease, diabetes, syphilis,
scurvy, or alcoholism, also impedes healing.
Infection by disease-producing micro-organisms or _pathogenic bacteria_
is, however, the most potent factor in disturbing the natural process of
repair in wounds.
SURGICAL BACTERIOLOGY
The influence of micro-organisms in the causation of disease, and the
rôle played by them in interfering with the natural process of repair,
are so important that the science of applied bacteriology has now come
to dominate every department of surgery, and it is from the standpoint
of bacteriology that nearly all surgical questions have to be
considered.
The term _sepsis_ as now used in clinical surgery no longer retains its
original meaning as synonymous with "putrefaction," but is employed to
denote all conditions in which bacterial infection has taken place, and
more particularly those in which pyogenic bacteria are present. In the
same way the term _aseptic_ conveys the idea of freedom from all forms
of bacteria, putrefactive or otherwise; and the term _antiseptic_ is
used to denote a power of counteracting bacteria and their products.
#General Characters of Bacteria.#--A _bacterium_ consists of a finely
granular mass of protoplasm, enclosed in a thin gelatinous envelope.
Many forms are motile--some in virtue of fine thread-like flagella, and
others through contractility of the protoplasm. The great majority
multiply by simple fission, each parent cell giving rise to two daughter
cells, and this process goes on with extraordinary rapidity. Other
varieties, particularly bacilli, are propagated by the formation of
_spores_. A spore is a minute mass of protoplasm surrounded by a dense,
tough membrane, developed in the interior of the parent cell. Spores are
remarkable for their tenacity of life, and for the resistance they offer
to the action of heat and chemical germicides.
Bacteria are most conveniently classified according to their shape. Thus
we recognise (1) those that are globular--_cocci_; (2) those that
resemble a rod--_bacilli_; (3) the spiral or wavy forms--_spirilla_.
_Cocci_ or _micrococci_ are minute round bodies, averaging about 1 µ in
diameter. The great majority are non-motile. They multiply by fission;
and when they divide in such a way that the resulting cells remain in
pairs, are called _diplococci_, of which the bacteria of gonorrhœa and
pneumonia are examples (Fig. 5). When they divide irregularly, and form
grape-like bunches, they are known as _staphylococci_, and to this
variety the commonest pyogenic or pus-forming organisms belong (Fig. 2).
When division takes place only in one axis, so that long chains are
formed, the term _streptococcus_ is applied (Fig. 3). Streptococci are
met with in erysipelas and various other inflammatory and suppurative
processes of a spreading character.
_Bacilli_ are rod-shaped bacteria, usually at least twice as long as
they are broad (Fig. 4). Some multiply by fission, others by
sporulation. Some forms are motile, others are non-motile. Tuberculosis,
tetanus, anthrax, and many other surgical diseases are due to different
forms of bacilli.
_Spirilla_ are long, slender, thread-like cells, more or less spiral or
wavy. Some move by a screw-like contraction of the protoplasm, some by
flagellæ. The spirochæte associated with syphilis (Fig. 36) is the most
important member of this group.
#Conditions of Bacterial Life.#--Bacteria require for their growth and
development a suitable food-supply in the form of proteins,
carbohydrates, and salts of calcium and potassium which they break up
into simpler elements. An alkaline medium favours bacterial growth; and
moisture is a necessary condition; spores, however, can survive the want
of water for much longer periods than fully developed bacteria. The
necessity for oxygen varies in different species. Those that require
oxygen are known as _aërobic bacilli_ or _aërobes_; those that cannot
live in the presence of oxygen are spoken of as _anaërobes_. The great
majority of bacteria, however, while they prefer to have oxygen, are
able to live without it, and are called _facultative anaërobes_.
The most suitable temperature for bacterial life is from 95° to 102° F.,
roughly that of the human body. Extreme or prolonged cold paralyses but
does not kill micro-organisms. Few, however, survive being raised to a
temperature of 134½° F. Boiling for ten to twenty minutes will kill all
bacteria, and the great majority of spores. Steam applied in an
autoclave under a pressure of two atmospheres destroys even the most
resistant spores in a few minutes. Direct sunlight, electric light, or
even diffuse daylight, is inimical to the growth of bacteria, as are
also Röntgen rays and radium emanations.
#Pathogenic Properties of Bacteria.#--We are now only concerned with
pathogenic bacteria--that is, bacteria capable of producing disease in
the human subject. This capacity depends upon two sets of factors--(1)
certain features peculiar to the invading bacteria, and (2) others
peculiar to the host. Many bacteria have only the power of living upon
dead matter, and are known as _saphrophytes_. Such as do nourish in
living tissue are, by distinction, known as _parasites_. The power a
given parasitic micro-organism has of multiplying in the body and giving
rise to disease is spoken of as its _virulence_, and this varies not
only with different species, but in the same species at different times
and under varying circumstances. The actual number of organisms
introduced is also an important factor in determining their pathogenic
power. Healthy tissues can resist the invasion of a certain number of
bacteria of a given species, but when that number is exceeded, the
organisms get the upper hand and disease results. When the organisms
gain access directly to the blood-stream, as a rule they produce their
effects more certainly and with greater intensity than when they are
introduced into the tissues.
Further, the virulence of an organism is modified by the condition of
the patient into whose tissues it is introduced. So long as a person is
in good health, the tissues are able to resist the attacks of moderate
numbers of most bacteria. Any lowering of the vitality of the
individual, however, either locally or generally, at once renders him
more susceptible to infection. Thus bruised or torn tissue is much more
liable to infection with pus-producing organisms than tissues clean-cut
with a knife; also, after certain diseases, the liability to infection
by the organisms of diphtheria, pneumonia, or erysipelas is much
increased. Even such slight depression of vitality as results from
bodily fatigue, or exposure to cold and damp, may be sufficient to turn
the scale in the battle between the tissues and the bacteria. Age is an
important factor in regard to the action of certain bacteria. Young
subjects are attacked by diphtheria, tuberculosis, acute osteomyelitis,
and some other diseases with greater frequency and severity than those
of more advanced years.
In different races, localities, environment, and seasons, the pathogenic
powers of certain organisms, such as those of erysipelas, diphtheria,
and acute osteomyelitis, vary considerably.
There is evidence that a _mixed infection_--that is, the introduction of
more than one species of organism, for example, the tubercle bacillus
and a pyogenic staphylococcus--increases the severity of the resulting
disease. If one of the varieties gain the ascendancy, the poisons
produced by the others so devitalise the tissue cells, and diminish
their power of resistance, that the virulence of the most active
organisms is increased. On the other hand, there is reason to believe
that the products of certain organisms antagonise one another--for
example, an attack of erysipelas may effect the cure of a patch of
tuberculous lupus.
Lastly, in patients suffering from chronic wasting diseases, bacteria
may invade the internal organs by the blood-stream in enormous numbers
and with great rapidity, during the period of extreme debility which
shortly precedes death. The discovery of such collections of organisms
on post-mortem examination may lead to erroneous conclusions being drawn
as to the cause of death.
#Results of Bacterial Growth.#--Some organisms, such as those of tetanus
and erysipelas, and certain of the pyogenic bacteria, show little
tendency to pass far beyond the point at which they gain an entrance to
the body. Others, on the contrary--for example, the tubercle bacillus
and the organism of acute osteomyelitis--although frequently remaining
localised at the seat of inoculation, tend to pass to distant parts,
lodging in the capillaries of joints, bones, kidney, or lungs, and there
producing their deleterious effects.
In the human subject, multiplication in the blood-stream does not occur
to any great extent. In some general acute pyogenic infections, such as
osteomyelitis, cellulitis, etc., pure cultures of staphylococci or of
streptococci may be obtained from the blood. In pneumococcal and typhoid
infections, also, the organisms may be found in the blood.
It is by the vital changes they bring about in the parts where they
settle that micro-organisms disturb the health of the patient. In
deriving nourishment from the complex organic compounds in which they
nourish, the organisms evolve, probably by means of a ferment, certain
chemical products of unknown composition, but probably colloidal in
nature, and known as _toxins_. When these poisons are absorbed into the
general circulation they give rise to certain groups of symptoms--such
as rise of temperature, associated circulatory and respiratory
derangements, interference with the gastro-intestinal functions and also
with those of the nervous system--which go to make up the condition
known as blood-poisoning, toxæmia, or _bacterial intoxication_. In
addition to this, certain bacteria produce toxins that give rise to
definite and distinct groups of symptoms--such as the convulsions of
tetanus, or the paralyses that follow diphtheria.
_Death of Bacteria._--Under certain circumstances, it would appear that
the accumulation of the toxic products of bacterial action tends to
interfere with the continued life and growth of the organisms
themselves, and in this way the natural cure of certain diseases is
brought about. Outside the body, bacteria may be killed by starvation,
by want of moisture, by being subjected to high temperature, or by the
action of certain chemical agents of which carbolic acid, the
perchloride and biniodide of mercury, and various chlorine preparations
are the most powerful.
#Immunity.#--Some persons are insusceptible to infection by certain
diseases, from which they are said to enjoy a _natural immunity_. In
many acute diseases one attack protects the patient, for a time at
least, from a second attack--_acquired immunity_.
_Phagocytosis._--In the production of immunity the leucocytes and
certain other cells play an important part in virtue of the power they
possess of ingesting bacteria and of destroying them by a process of
intra-cellular digestion. To this process Metchnikoff gave the name of
_phagocytosis_, and he recognised two forms of _phagocytes_: (1) the
_microphages_, which are the polymorpho-nuclear leucocytes of the blood;
and (2) the _macrophages_, which include the larger hyaline leucocytes,
endothelial cells, and connective-tissue corpuscles.
During the process of phagocytosis, the polymorpho-nuclear leucocytes in
the circulating blood increase greatly in numbers (_leucocytosis_), as
well as in their phagocytic action, and in the course of destroying the
bacteria they produce certain ferments which enter the blood serum.
These are known as _opsonins_ or _alexins_, and they act on the bacteria
by a process comparable to narcotisation, and render them an easy prey
for the phagocytes.
_Artificial or Passive Immunity._--A form of immunity can be induced by
the introduction of protective substances obtained from an animal which
has been actively immunised. The process by which passive immunity is
acquired depends upon the fact that as a result of the reaction between
the specific virus of a particular disease (the _antigen_) and the
tissues of the animal attacked, certain substances--_antibodies_--are
produced, which when transferred to the body of a susceptible animal
protect it against that disease. The most important of these antibodies
are the _antitoxins_. From the study of the processes by which immunity
is secured against the effects of bacterial action the serum and vaccine
methods of treating certain infective diseases have been evolved. The
_serum treatment_ is designed to furnish the patient with a sufficiency
of antibodies to neutralise the infection. The anti-diphtheritic and the
anti-tetanic act by neutralising the specific toxins of the
disease--_antitoxic serums_; the anti-streptcoccic and the serum for
anthrax act upon the bacteria--_anti-bacterial serums_.
A _polyvalent_ serum, that is, one derived from an animal which has been
immunised by numerous strains of the organism derived from various
sources, is much more efficacious than when a single strain has been
used.
_Clinical Use of Serums._--Every precaution must be taken to prevent
organismal contamination of the serum or of the apparatus by means of
which it is injected. Syringes are so made that they can be sterilised
by boiling. The best situations for injection are under the skin of the
abdomen, the thorax, or the buttock, and the skin should be purified at
the seat of puncture. If the bulk of the full dose is large, it should
be divided and injected into different parts of the body, not more than
20 c.c. being injected at one place. The serum may be introduced
directly into a vein, or into the spinal canal, _e.g._ anti-tetanic
serum. The immunity produced by injections of antitoxic sera lasts only
for a comparatively short time, seldom longer than a few weeks.
_"Serum Disease" and Anaphylaxis._--It is to be borne in mind that some
patients exhibit a supersensitiveness with regard to protective sera, an
injection being followed in a few days by the appearance of an
urticarial or erythematous rash, pain and swelling of the joints, and a
variable degree of fever. These symptoms, to which the name _serum
disease_ is applied, usually disappear in the course of a few days.
The term _anaphylaxis_ is applied to an allied condition of
supersensitiveness which appears to be induced by the injection of
certain substances, including toxins and sera, that are capable of
acting as antigens. When a second injection is given after an interval
of some days, if anaphylaxis has been established by the first dose, the
patient suddenly manifests toxic symptoms of the nature of profound
shock which may even prove fatal. The conditions which render a person
liable to develop anaphylaxis and the mechanism by which it is
established are as yet imperfectly understood.
_Vaccine Treatment._--The vaccine treatment elaborated by A. E. Wright
consists in injecting, while the disease is still active, specially
prepared dead cultures of the causative organisms, and is based on the
fact that these "vaccines" render the bacteria in the tissues less able
to resist the attacks of the phagocytes. The method is most successful
when the vaccine is prepared from organisms isolated from the patient
himself, _autogenous vaccine_, but when this is impracticable, or takes
a considerable time, laboratory-prepared polyvalent _stock vaccines_ may
be used.
_Clinical Use of Vaccines._--Vaccines should not be given while a
patient is in a negative phase, as a certain amount of the opsonin in
the blood is used up in neutralising the substances injected, and this
may reduce the opsonic index to such an extent that the vaccines
themselves become dangerous. As a rule, the propriety of using a vaccine
can be determined from the general condition of the patient. The initial
dose should always be a small one, particularly if the disease is acute,
and the subsequent dosage will be regulated by the effect produced. If
marked constitutional disturbance with rise of temperature follows the
use of a vaccine, it indicates a negative phase, and calls for a
diminution in the next dose. If, on the other hand, the local as well as
the general condition of the patient improves after the injection, it
indicates a positive phase, and the original dose may be repeated or
even increased. Vaccines are best introduced subcutaneously, a part
being selected which is not liable to pressure, as there is sometimes
considerable local reaction. Repeated doses may be necessary at
intervals of a few days.
The vaccine treatment has been successfully employed in various
tuberculous lesions, in pyogenic infections such as acne, boils,
sycosis, streptococcal, pneumococcal, and gonococcal conditions, in
infections of the accessory air sinuses, and in other diseases caused by
bacteria.
PYOGENIC BACTERIA
From the point of view of the surgeon the most important varieties of
micro-organisms are those that cause inflammation and suppuration--the
_pyogenic bacteria_. This group includes a great many species, and these
are so widely distributed that they are to be met with under all
conditions of everyday life.
The nature of the inflammatory and suppurative processes will be
considered in detail later; suffice it here to say that they are brought
about by the action of one or other of the organisms that we have now to
consider.
It is found that the _staphylococci_, which cluster into groups, tend to
produce localised lesions; while the chain-forms--_streptococci_--give
rise to diffuse, spreading conditions. Many varieties of pyogenic
bacteria have now been differentiated, the best known being the
staphylococcus aureus, the streptococcus, and the bacillus coli
communis.
[Illustration: FIG. 2.--Staphylococcus aureus in Pus from case of
Osteomyelitis. × 1000 diam. Gram's stain.]
_Staphylococcus Aureus._--This is the commonest organism found in
localised inflammatory and suppurative conditions. It varies greatly in
its virulence, and is found in such widely different conditions as skin
pustules, boils, carbuncles, and some acute inflammations of bone. As
seen by the microscope it occurs in grape-like clusters, fission of the
individual cells taking place irregularly (Fig. 2). When grown in
artificial media, the colonies assume an orange-yellow colour--hence the
name _aureus_. It is of high vitality and resists more prolonged
exposure to high temperatures than most non-sporing bacteria. It is
capable of lying latent in the tissues for long periods, for example, in
the marrow of long bones, and of again becoming active and causing a
fresh outbreak of suppuration. This organism is widely distributed: it
is found on the skin, in the mouth, and in other situations in the body,
and as it is present in the dust of the air and on all objects upon
which dust has settled, it is a continual source of infection unless
means are taken to exclude it from wounds.
The _staphylococcus albus_ is much less common than the aureus, but has
the same properties and characters, save that its growth on artificial
media assumes a white colour. It is the common cause of stitch
abscesses, the skin being its normal habitat.
[Illustration: FIG. 3.--Streptococci in Pus from an acute abscess in
subcutaneous tissue. × 1000 diam. Gram's stain.]
_Streptococcus Pyogenes._--This organism also varies greatly in its
virulence; in some instances--for example in erysipelas--it causes a
sharp attack of acute spreading inflammation, which soon subsides
without showing any tendency to end in suppuration; under other
conditions it gives rise to a generalised infection which rapidly proves
fatal. The streptococcus has less capacity of liquefying the tissues
than the staphylococcus, so that pus formation takes place more slowly.
At the same time its products are very potent in destroying the tissues
in their vicinity, and so interfering with the exudation of leucocytes
which would otherwise exercise their protective influence. Streptococci
invade the lymph spaces, and are associated with acute spreading
conditions such as phlegmonous or erysipelatous inflammations and
suppurations, lymphangitis and suppuration in lymph glands, and
inflammation of serous and synovial membranes, also with a form of
pneumonia which is prone to follow on severe operations in the mouth and
throat. Streptococci are also concerned in the production of spreading
gangrene and pyæmia.
Division takes place in one axis, so that chains of varying length are
formed (Fig. 3). It is less easily cultivated by artificial media than
the staphylococcus; it forms a whitish growth.
[Illustration: FIG. 4.--Bacillus coli communis in Urine, from a case of
Cystitis. × 1000 diam. Leishman's stain.]
_Bacillus Coli Communis._--This organism, which is a normal inhabitant
of the intestinal tract, shows a great tendency to invade any organ or
tissue whose vitality is lowered. It is causatively associated with such
conditions as peritonitis and peritoneal suppuration resulting from
strangulated hernia, appendicitis, or perforation in any part of the
alimentary canal. In cystitis, pyelitis, abscess of the kidney,
suppuration in the bile-ducts or liver, and in many other abdominal
conditions, it plays a most important part. The discharge from wounds
infected by this organism has usually a fœtid, or even a fæcal odour,
and often contains gases resulting from putrefaction.
It is a small rod-shaped organism with short flagellæ, which render it
motile (Fig. 4). It closely resembles the typhoid bacillus, but is
distinguished from it by its behaviour in artificial culture media.
[Illustration: FIG. 5.--Fraenkel's Pneumococci in Pus from Empyema
following Pneumonia. × 100 diam. Stained with Muir's capsule stain.]
_Pneumo-bacteria._--Two forms of organism associated with
pneumonia--_Fraenkel's pneumococcus_ (one of the diplococci) (Fig. 5)
and _Friedländer's pneumo-bacillus_ (a short rod-shaped form)--are
frequently met with in inflammations of the serous and synovial
membranes, in suppuration in the liver, and in various other
inflammatory and suppurative conditions.
_Bacillus Typhosus._--This organism has been found in pure culture in
suppurative conditions of bone, of cellular tissue, and of internal
organs, especially during convalescence from typhoid fever. Like the
staphylococcus, it is capable of lying latent in the tissues for long
periods.
_Other Pyogenic Bacteria._--It is not necessary to do more than name
some of the other organisms that are known to be pyogenic, such as the
bacillus pyocyaneus, which is found in green and blue pus, the
micrococcus tetragenus, the gonococcus, actinomyces, the glanders
bacillus, and the tubercle bacillus. Most of these will receive further
mention in connection with the diseases to which they give rise.
#Leucocytosis.#--Most bacterial diseases, as well as certain other
pathological conditions, are associated with an increase in the number
of leucocytes in the blood throughout the circulatory system. This
condition of the blood, which is known as _leucocytosis_, is believed to
be due to an excessive output and rapid formation of leucocytes by the
bone marrow, and it probably has as its object the arrest and
destruction of the invading organisms or toxins. To increase the
resisting power of the system to pathogenic organisms, an artificial
leucocytosis may be induced by subcutaneous injection of a solution of
nucleinate of soda (16 minims of a 5 per cent. solution).
The _normal_ number of leucocytes per cubic millimetre varies in
different individuals, and in the same individual under different
conditions, from 5000 to 10,000: 7500 is a normal average, and anything
above 12,000 is considered abnormal. When leucocytosis is present, the
number may range from 12,000 to 30,000 or even higher; 40,000 is looked
upon as a high degree of leucocytosis. According to Ehrlich, the
following may be taken as the standard proportion of the various forms
of leucocytes in normal blood: polynuclear neutrophile leucocytes, 70 to
72 per cent.; lymphocytes, 22 to 25 per cent.; eosinophile cells, 2 to 4
per cent.; large mononuclear and transitional leucocytes, 2 to 4 per
cent.; mast-cells, 0.5 to 2 per cent.
In estimating the clinical importance of a leucocytosis, it is not
sufficient merely to count the aggregate number of leucocytes present. A
differential count must be made to determine which variety of cells is
in excess. In the majority of surgical affections it is chiefly the
granular polymorpho-nuclear neutrophile leucocytes that are in excess
(_ordinary leucocytosis_). In some cases, and particularly in parasitic
diseases such as trichiniasis and hydatid disease, the eosinophile
leucocytes also show a proportionate increase (_eosinophilia_). The term
_lymphocytosis_ is applied when there is an increase in the number of
circulating lymphocytes, as occurs, for example, in lymphatic leucæmia,
and in certain cases of syphilis.
Leucocytosis is met with in nearly all acute infective diseases, and in
acute pyogenic inflammatory affections, particularly in those attended
with suppuration. In exceptionally acute septic conditions the extreme
virulence of the toxins may prevent the leucocytes reacting, and
leucocytosis may be absent. The absence of leucocytosis in a disease in
which it is usually present is therefore to be looked upon as a grave
omen, particularly when the general symptoms are severe. In some cases
of malignant disease the number of leucocytes is increased to 15,000 or
20,000. A few hours after a severe hæmorrhage also there is usually a
leucocytosis of from 15,000 to 30,000, which lasts for three or four
days (Lyon). In cases of hæmorrhage the leucocytosis is increased by
infusion of fluids into the circulation. After all operations there is
at least a transient leucocytosis (_post-operative leucocytosis_)
(F. I. Dawson).
The leucocytosis begins soon after the infection manifests itself--for
example, by shivering, rigor, or rise of temperature. The number of
leucocytes rises somewhat rapidly, increases while the condition is
progressing, and remains high during the febrile period, but there is no
constant correspondence between the number of leucocytes and the height
of the temperature. The arrest of the inflammation and its resolution
are accompanied by a fall in the number of leucocytes, while the
occurrence of suppuration is attended with a further increase in their
number.
In interpreting the "blood count," it is to be kept in mind that a
_physiological leucocytosis_ occurs within three or four hours of taking
a meal, especially one rich in proteins, from 1500 to 2000 being added
to the normal number. In this _digestion leucocytosis_ the increase is
chiefly in the polynuclear neutrophile leucocytes. Immediately before
and after delivery, particularly in primiparæ, there is usually a
moderate degree of leucocytosis. If the labour is normal and the
puerperium uncomplicated, the number of leucocytes regains the normal in
about a week. Lactation has no appreciable effect on the number of
leucocytes. In new-born infants the leucocyte count is abnormally high,
ranging from 15,000 to 20,000. In children under one year of age, the
normal average is from 10,000 to 20,000.
_Absence of Leucocytosis--Leucopenia._--In certain infective diseases
the number of leucocytes in the circulating blood is abnormally
low--3000 or 4000--and this condition is known as _leucopenia_. It
occurs in typhoid fever, especially in the later stages of the disease,
in tuberculous lesions unaccompanied by suppuration, in malaria, and in
most cases of uncomplicated influenza. The occurrence of leucocytosis in
any of these conditions is to be looked upon as an indication that a
mixed infection has taken place, and that some suppurative process is
present.
The absence of leucocytosis in some cases of virulent septic poisoning
has already been referred to.
It will be evident that too much reliance must not be placed upon a
single observation, particularly in emergency cases. Whenever possible,
a series of observations should be made, the blood being examined about
four hours after meals, and about the same hour each day.
The clinical significance of the blood count in individual diseases will
be further referred to.
_The Iodine or Glycogen Reaction._--The leucocyte count may be
supplemented by staining films of the blood with a watery solution of
iodine and potassium iodide. In all advancing purulent conditions, in
septic poisonings, in pneumonia, and in cancerous growths associated
with ulceration, a certain number of the polynuclear leucocytes are
stained a brown or reddish-brown colour, due to the action of the iodine
on some substance in the cells of the nature of glycogen. This reaction
is absent in serous effusions, in unmixed tuberculous infections, in
uncomplicated typhoid fever, and in the early stages of cancerous
growths.