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The Story Of Germ Life

H >> H. W. Conn >> The Story Of Germ Life




From the facts just stated it will be evident that any list of
germ diseases will be rather uncertain. Still, the studies of the
last twenty years or more have disclosed some definite relations
of bacteria and disease, and a list of the diseases more or less
definitely associated with distinct species of bacteria is of
interest. Such a list, including only well-known diseases, is as
follows:

Name of disease. Name of bacterium producing the disease.
Anthrax (Malignant pustule). Bacillus anthracis.
Cholera. Spirillum cholera: asiaticae
Croupous pneumonia. Micrococcus pneumonia crouposa.
Diphtheria. Bacillus diphtheria.
Glanders. Bacillus mallei.
Gonorrhoea. Micrococcus gonorrhaeae
Influenza. Bacillus of influenza.
Leprosy. Bacillus leprae.
Relapsing fever. Spirillum Obermeieri.
Tetanus (lockjaw). Bacillus tetani.
Tuberculosis (including
consumption, scrofula, etc.) Bacillus tuberculosis.
Typhoid fever. Bacillus typhi abdominalis.

Various wound infections, including septicaemia, pyaemia, acute
abscesses, ulcers, erysipelas, etc., are produced by a few forms
of micrococci, resembling each other in many points but differing
slightly. They are found almost indiscriminately in any of these
wound infections, and none of them appears to have any definite
relation to any special form of disease unless it be the
micrococcus of erysipelas. The common pus micrococci are grouped
under three species, Staphylococcus pyogenes aureus,
Staphylococcus pyogenes, and Streptococcus pyogenes. These three
are the most common, but others are occasionally found.

In addition to these, which may be regarded as demonstrated, the
following diseases are with more or less certainty regarded as
caused by distinct specific bacteria: Bronchitis, endocarditis,
measles, whooping-cough, peritonitis, pneumonia, syphilis.

Still another list might be given of diseases whose general nature
indicates that they are caused by bacteria, but in connection with
which no distinct bacterium has yet been found. As might be
expected also, a larger list of animal diseases has been
demonstrated to be caused by these organisms. In addition, quite a
number of species of bacteria have been found in such material as
faeces, putrefying blood, etc., which have been shown by
experiment to be capable of producing diseases in animals, but in
regard to which we have no evidence that they ever do produce
actual disease under any normal conditions. These may contribute,
perhaps, to the troubles arising from poisonous foods, but can not
be regarded as disease germs proper.

VARIABILITY OF PATHOGENIC POWERS.

As has already been stated, our ideas of the relation of bacteria
to disease have undergone quite a change since they were first
formulated, and we recognise other factors influencing disease
besides the actual presence of the bacterium. These we may briefly
consider under two heads, viz., variation in the bacterium, and
variation in the susceptibility of the individual. The first will
require only a brief consideration.

That the same species of pathogenic bacteria at different times
varies in its powers to produce disease has long been known.
Various conditions are known to affect thus the virulence of
bacteria. The bacillus which is supposed to give rise to pneumonia
loses its power to produce the disease after having been
cultivated for a short time in ordinary culture media in the
laboratory. This is easily understood upon the suggestion that it
is a parasitic bacillus and does not thrive except under parasitic
conditions. Its pathogenic powers can sometimes be restored by
passing it again through some susceptible animal. One of the most
violent pathogenic bacteria is that which produces anthrax, but
this loses its pathogenic powers if it is cultivated for a
considerable period at a high temperature. The micrococcus which
causes fowl cholera loses its power if it be cultivated in common
culture media, care being taken to allow several days to elapse
between the successive inoculations into new culture flasks. Most
pathogenic bacteria can in some way be so treated as to suffer a
diminution or complete loss of their powers of producing a fatal
disease. On the other hand, other conditions will cause an
increase in the virulence of a pathogenic germ. The virus which
produces hydrophobia is increased in violence if it is inoculated
into a rabbit and subsequently taken from the rabbit for further
inoculation. The fowl cholera micrococcus, which has been weakened
as just mentioned, may be restored to its original violence by
inoculating it into a small bird, like a sparrow, and inoculating
a second bird from this. A few such inoculations will make it as
active as ever. These variations doubtless exist among the species
in Nature as well as in artificial cultures. The bacteria which
produce the various wound infections and abscesses, etc., appear
to vary under normal conditions from a type capable of producing
violent and fatal blood poisoning to a type producing only a
simple abscess, or even to a type that is entirely innocuous. It
is this factor, doubtless, which in a large measure determines the
severity of any epidemic of a bacterial contagious disease.

SUSCEPTIBILITY OF THE INDIVIDUAL.

The very great modification of our early views has affected our
ideas as to the power which individuals have of resisting the
invasion of pathogenic bacteria. It has from the first been
understood that some individuals are more susceptible to disease
than others, and in attempting to determine the significance of
this fact many valuable and interesting discoveries have been
made. After the exposure to the disease there follows a period of
some length in which there are no discernible effects. This is
followed by the onset of the disease and its development to a
crisis, and, if this be passed, by a recovery. The general course
of a germ disease is divided into three stages: the stage of
incubation, the development of the disease, and the recovery. The
susceptibility of the body to a disease may be best considered
under the three heads of Invasion, Resistance, Recovery.

Means of Invasion.--In order that a germ disease should arise in
an individual, it is first necessary that the special bacterium
which causes the disease should get into the body. There are
several channels through which bacteria can thus find entrance;
these are through the mouth, through the nose, through the skin,
and occasionally through excretory ducts. Those which come through
the mouth come with the food or drink which we swallow; those
which enter through the nose must be traced to the air; and those
which enter through the skin come in most cases through contact
with some infected object, such as direct contact with the body of
an infected person or his clothing or some objects he has handled,
etc. Occasionally, perhaps, the bacteria may get into the skin
from the air, but this is certainly uncommon and confined to a few
diseases. There are here two facts of the utmost importance for
every one to understand: first, that the chance of disease
bacteria being carried to us through the air is very slight and
confined to a few diseases, such as smallpox, tuberculosis,
scarlet fever; etc., and, secondly, that the uninjured skin and
the uninjured mucous membrane also is almost a sure protection
against the invasion of the bacteria. If the skin is whole,
without bruises or cuts, bacteria can seldom, if ever, find
passage through it. These two facts are of the utmost importance,
since of all sources of infection we have the least power to guard
against infection through the air, and since of all means 'of
entrance we can guard the skin with the greatest difficulty. We
can easily render food free from pathogenic bacteria by heating
it. The material we drink can similarly be rendered harmless, but
we can not by any known means avoid breathing air, nor is there
any known method of disinfecting the air, and it is impossible for
those who have anything to do with sick persons to avoid entirely
having contact either with the patient or with infected clothing
or utensils.

From the facts here given it will be seen that the individual's
susceptibility to disease produced by parasitic bacteria will
depend upon his habits of cleanliness, his care in handling
infectious material, or care in cleansing the hands after such
handling, upon his habit of eating food cooked or raw, and upon
the condition of his skin and mucous membranes, since any kind of
bruises will increase susceptibility. Slight ailments, such as
colds, which inflame the mucous membrane, will decrease its
resisting power and render the individual more susceptible to the
entrance of any pathogenic germs should they happen to be present.
Sores in the mouth or decayed teeth may in the same way be
prominent factors in the individual's susceptibility. Thus quite a
number of purely physical factors may contribute to an
individual's susceptibility.

Resisting Power of the Body.--Even after the bacteria get into the
body it is by no means certain that they will give rise to
disease, for they have now a battle to fight before they can be
sure of holding their own. It is now, indeed, that the actual
conflict between the powers of the body and these microscopic
invaders begins. After they have found entrance into the body the
bacteria have arrayed against them strong resisting forces of the
human organism, endeavouring to destroy and expel them. Many of
them are rapidly killed, and sometimes they are all destroyed
without being able to gain a foothold. In such cases, of course,
no trouble results. In other cases the body fails to overcome the
powers of the invaders and they eventually multiply rapidly. In
this struggle the success of the invaders is not necessarily a
matter of numbers. They are simply struggling to gain a position
in the body, where they can feed and grow. A few individuals may
be entirely sufficient to seize such a foothold, and then these by
multiplying may soon become indefinitely numerous. To protect
itself, therefore, the human body must destroy every individual
bacterium, or at least render them all incapable of growth. Their
marvellous reproductive powers give the bacteria an advantage in
the battle. On the other hand, it takes time even for these
rapidly multiplying beings to become sufficiently numerous to do
injury. There is thus an interval after their penetration into the
body when these invaders are weak in numbers. During this
interval--the period of incubation--the body may organize a
resistance sufficient to expel them.

We do not as yet thoroughly understand the forces which the human
organism is able to array against these invading foes. Some of its
methods of defence are, however, already intelligible to us, and
we know enough, at all events, to give us an idea of the intensity
of the conflict that is going on, and of the vigorous and powerful
forces which the human organism is able to bring against its
invading enemies.

In the first place, we notice that a majority of bacteria are
utterly unable to grow in the human body even if they do find
entrance. There are known to bacteriologists to-day many hundreds,
even thousands of species, but the vast majority of these find in
the human tissues conditions so hostile to their life that they
are utterly unable to grow therein. Human flesh or human blood
will furnish excellent food for them if the individual be dead,
but living human flesh and blood in some way exerts a repressing
influence upon them which is fatal to the growth of a vast
majority of species. Some few species, however, are not thus
destroyed by the hostile agencies of the tissues of the animal,
but are capable of growing and multiplying in the living body.
These alone are what constitute the pathogenic bacteria, since, of
course, these are the only bacteria which can produce disease by
growing in the tissues of an animal. The fact that the vast
majority of bacteria can not grow in the living organism shows
clearly enough that there are some conditions existing in the
living tissue hostile to bacterial life. There can be little
doubt, moreover, that it is these same hostile conditions, which
enable the body to resist the attack of the pathogenic species in
cases where resistance is successfully made.

What are the forces arrayed against these invaders? The essential
nature of the battle appears to be a production of poisons and
counter poisons. It appears to be an undoubted fact that the first
step in repelling these bacteria is to flood them with certain
poisons which check their growth. In the blood and lymph of man
and other animals there are present certain products which have a
direct deleterious influence upon the growth of micro-organisms.
The existence of these poisons is undoubted, many an experiment
having directly attested to their presence in the blood of
animals. Of their nature we know very little, but of their
repressing influence upon bacterial growth we are sure. They have
been named alexines, and they are produced in the living tissue,
although as to the method of their production we are in ignorance.
By the aid of these poisons the body is able to prevent the growth
of the vast majority of bacteria which get into its tissues.
Ordinary micro-organisms are killed at once, for these alexines
act as antiseptics, and common bacteria can no more grow in the
living body than they could in a solution containing other poisons
Thus the body has a perfect protection against the majority of
bacteria. The great host of species which are found in water,
milk, air, in our mouths or clinging to our skin, and which are
almost omnipresent in Nature, are capable of growing well enough
in ordinary lifeless organic foods, but just as soon as they
succeed in finding entrance into living human tissue their growth
is checked at once by these antiseptic agents which are poured
upon them. Such bacteria are therefore not pathogenic germs, and
not sources of trouble to human health.

There are, on the other hand, a few species of bacteria which may
be able to retain their lodgment in the body m spite of this
attempt of the individual to get rid of them. These, of course,
constitute the pathogenic species, or so called "disease germs".
Only such species as can overcome this first resistance can be
disease germs, for they alone can retain their foothold in the
body.

But how do these species overcome the poisons, which kill the
other harmless bacteria? They, as well as the harmless forms, find
these alexines injurious to their growth, but in some way they are
able to counteract the poisons. In this general discussion of
poisons we are dealing with a subject which is somewhat obscure,
but apparently the pathogenic bacteria are able to overcome the
alexines of the body by producing in their turn certain other
products which neutralize the alexines, thus annulling their
action. These pathogenic bacteria, when they get into the body,
give rise at once to a group of bodies which have been named
lysines. These lysines are as mysterious to us as the alexines,
but they neutralize the effect of the alexines and thus overcome
the resistance the body offers to bacterial growth The invaders
can now multiply rapidly enough to get a lasting foothold in the
body and then soon produce the abnormal symptoms which we call
disease Pathogenic bacteria thus differ from the non-pathogenic
bacteria primarily in this power of secreting products which can
neutralize the ordinary effects of the alexines, and so overcome
the body's normal resistance to their parasitic life.

Even if the bacteria do thus overcome the alexines the battle is
not yet over, for the individual has another method of defence
which is now brought into activity to check the growth of the
invading organisms. This second method of resistance is by means
of a series of active cells found in the blood, known as white
blood-corpuscles (Fig. 33 a, b). They are minute bits of
protoplasm present in the blood and lymph in large quantities.
They are active cells, capable of locomotion and able to crawl out
of the blood-vessels Not infrequently they are found to take into
their bodies small objects with which they come in contact. One of
their duties is thus to engulf minute irritating bodies which may
be in the tissues, and to carry them away for excretion. They thus
act as scavengers These corpuscles certainly have some agency in
warding off the attacks of pathogenic bacteria Very commonly they
collect in great numbers in the region of the body where invading
bacteria are found. Such invading bacteria exist upon them a
strong attraction, and the corpuscles leave the blood-vessels and
sometimes form a solid phalanx completely surrounding the invading
germs. Their collection at these points may make itself seen
externally by the phenomenon we call inflammation.

There is no question that the corpuscles engage in conflict with
the bacteria when they thus surround them. There has been not a
little dispute, however, as to the method by which they carry on
the conflict. It has been held by some that the corpuscles
actually take the bacteria into their bodies, swallow them, as it
were, and subsequently digest them (Fig. 33 c, d, e). This idea
gave rise to the theory of phagocytosis, and the corpuscles were
consequently named phagocytes. The study of several years has,
however, made it probable that this is not the ordinary method by
which the corpuscles destroy the bacteria. According to our
present knowledge the method is a chemical one. These cells, when
they thus collect in quantities around the invaders, appear to
secrete from their own bodies certain injurious products which act
upon the bacteria much as do the alexines already mentioned. These
new bodies have a decidedly injurious effect upon the multiplying
bacteria; they rapidly check their growth, and, acting in union
with the alexines, may perhaps entirely destroy them.

After the bacteria are thus killed, the white blood-corpuscles may
load themselves with their dead bodies and carry them away (Fig.
33 d, e). Sometimes they pass back into the blood stream and carry
the bacteria to various parts of the body for elimination. Not
infrequently the white corpuscles die in the contest, and then may
accumulate in the form of pus and make their way through the skin
to be discharged directly. The battle between these phagocytes and
the bacteria goes on vigorously. If in the end the phagocytes
prove too strong for the invaders, the bacteria are gradually all
destroyed, and the attack is repelled. Under these circumstances
the individual commonly knows nothing--of the matter. This
conflict has taken place entirely without any consciousness on his
part, and he may not even know that he has been exposed to the
attack of the bacteria. In other cases the bacteria prove too
strong for the phagocytes. They multiply too rapidly, and
sometimes they produce secretions which actually drive the
phagocytes away. Commonly, as already noticed, the corpuscles are
attracted to the point of invasion, but in some cases, when a
particularly deadly and vigorous species of bacteria invades the
body, the secretions produced by them are so powerful as actually
to drive the corpuscles away. Under these circumstances the
invading hosts have a chance to multiply unimpeded, to distribute
themselves over the body, and the disease rapidly follows as the
result of their poisoning action on the body tissues.

It is plain, then, that the human body is not helpless in the
presence of the bacteria of disease, but that it is supplied with
powerful resistant forces. It must not be supposed, however, that
the outline of the action of these forces just given is anything
like a complete account of the matter; nor must it be inferred
that the resistance is in all respects exactly as outlined. The
subject has only recently been an object of investigation, and we
are as yet in the dark in regard to many of the facts. The future
may require us to modify to some extent even the brief outline
which has been given. But while we recognise this uncertainty in
the details, we may be assured of the general facts. The living
body has some very efficacious resistant forces which prevent most
bacteria from growing within its tissues, and which in large
measure may be relied upon to drive out the true pathogenic
bacteria. These resistant forces are in part associated with the
productions of body poisons, and are in part associated with the
active powers of special cells which have been called phagocytes.
The origin of the poisons and the exact method of action of the
phagocytes we may well leave to the future to explain.

These resisting powers of the body will vary with conditions. It
is evident that they are natural powers, and they will doubtless
vary with the general condition of vigour of the individual.
Robust health, a body whose powers are strong, well nourished, and
vigorous, will plainly furnish the conditions for the greatest
resistance to bacterial diseases. One whose bodily activities are
weakened by poor nutrition can offer less resistance. The question
whether one shall suffer from a germ disease is not simply the
question whether he shall be exposed, or even the question whether
the bacteria shall find entrance into his body. It is equally
dependent upon whether he has the bodily vigour to produce
alexines in proper quantity, or to summon the phagocytes in
sufficient abundance and vigour to ward off the attack. We may do
much to prevent disease by sanitation, which aids in protecting
the individual from attack; but we must not forget that the other
half of the battle is of equal importance, and hence we must do
all we can to strengthen the resisting forces of the organism.

RECOVERY FROM GERM DISEASES.

These resisting forces are not always sufficient to drive off the
invaders. The organisms may retain their hold in the body for a
time and eventually break down the resistance. After this they may
multiply unimpeded and take entire possession of the body. As they
become more numerous their poisonous products increase and begin
to produce direct poisoning effects on the body. The incubation
period is over and the disease comes on. The disease now runs its
course. It becomes commonly more and more severe until a crisis is
reached. Then, unless the poisoning is so severe that death
occurs, the effects pass away and recovery takes place.

But why should not a germ disease be always fatal? If the bacteria
thus take possession of the body and can grow there, why do they
not always continue to multiply until they produce sufficient
poison to destroy the life of the individual? Such fatal results
do, of course, occur, but in by far the larger proportion of cases
recovery finally takes place.

Plainly, the body must have another set of resisting forces which
is concerned in the final recovery. Although weakened by the
poisoning and suffering from the disease, it does not yield the
battle, but somewhat slowly organizes a new attack upon the
invaders. For a time the multiplying bacteria have an unimpeded
course and grow rapidly; but finally their further increase is
checked, their vigour impaired, and after this they diminish in
numbers and are finally expelled from the body entirely. Of the
nature of this new resistance but little is yet known. We notice,
in the first place, that commonly after such a recovery the
individual has decidedly increased resistance to the disease. This
increased resistance may be very lasting, and may be so
considerable as to give almost complete immunity from the disease
for many years, or for life. One attack of scarlet fever gives the
individual great immunity for the future. On the other hand, the
resistance thus derived may be very temporary, as in the case of
diphtheria. But a certain amount of resistance appears to be
always acquired. This power of resisting the activities of the
parasites seems to be increased during the progress of the
disease, and, if it becomes sufficient, it finally drives off the
bacteria before they have produced death. After this, recovery
takes place. To what this newly acquired resisting power is due is
by no means clear to bacteriologists, although certain factors
are already known. It appears beyond question that in the case of
certain diseases the cells of the body after a time produce
substances which serve as antidotes to the poisons produced by the
bacteria during their growth in the body-antitoxines. In the case
of diphtheria, for instance, the germs growing in the throat
produce poisons which are absorbed by the body and give rise to
the symptoms of the disease; but after a time the body cells
react, and themselves produce a counter toxic body which
neutralizes the poisonous effect of the diphtheria poison. This
substance has been isolated from the blood of animals that have
recovered from an attack of diphtheria, and has been called
diphtheria antitoxine. But even with this knowledge the recovery
is not fully explained. This antitoxine neutralizes the effects of
the diphtheria toxine, and then the body develops strength to
drive off the bacteria which have obtained lodgment in the throat.
How they accomplish this latter achievement we do not know as yet.
The antitoxme developed simply neutralizes the effects of the
toxine. Some other force must be at work to get rid of the
bacteria, a force which can only exert itself after the poisoning
effect of the poison is neutralized. In these cases, then, the
recovery is due, first, to the development in the body of the
natural antidotes to the toxic poisons, and, second, to some other
unknown force which drives off the parasites.

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