METHODS OF COMBATING PARASITIC BACTERIA.
The chief advantage of knowing the cause of disease is that it
gives us a vantage ground from which we may hope to find means of
avoiding its evils. The study of medicine in the past history of
the world has been almost purely empirical, with a very little of
scientific basis. Great hopes are now entertained that these new
facts will place this matter upon a more strictly scientific
foundation. Certainly in the past twenty-five years, since
bacteriology has been studied, more has been done to solve
problems connected with disease than ever before. This new
knowledge has been particularly directed toward means of avoiding
disease. Bacteriology has thus far borne fruit largely in the line
of preventive medicine, although to a certain extent also along
the line of curative medicine. This chapter will be devoted to
considering how the study of bacteriology has contributed directly
and indirectly to our power of combating disease.
PREVENTIVE MEDICINE.
In the study of medicine in the past centuries the only aim has
been to discover methods of curing disease; at the present time a
large and increasing amount of study is devoted to the methods of
preventing disease. Preventive medicine is a development of the
last few years, and is based almost wholly upon our knowledge of
bacteria. This subject is yearly becoming of more importance.
Forewarned is forearmed, and it has been found that to know the
cause of a disease is a long step toward avoiding it. As some of
our contagious and epidemic diseases have been studied in the
light of bacteriological knowledge, it has been found possible to
determine not only their cause, but also how infection is brought
about, and consequently how contagion may be avoided. Some of the
results which have grown up so slowly as to be hardly appreciated
are really great triumphs. For instance, the study of bacteriology
first led us to suspect, and then demonstrated, that tuberculosis
is a contagious disease, and from the time that this was thus
proved there has been a slow, but, it is hoped, a sure decline in
this disease. Bacteriological study has shown that the source of
cholera infection in cases of raging epidemics is, in large part
at least, our drinking water; and since this has been known,
although cholera has twice invaded Europe, and has been widely
distributed, it has not obtained any strong foothold or given rise
to any serious epidemic except in a few cases where its ravages
can be traced to recognised carelessness. It is very significant
to compare the history of the cholera epidemics of the past few
years with those of earlier dates. In the epidemics of earlier
years the cholera swept ruthlessly through communities without
check. In the last few years, although it has repeatedly knocked
at the doors of many European cities, it has been commonly
confined to isolated cases, except in a few instances where these
facts concerning the relation to drinking water were ignored.
The study of preventive medicine is yet in its infancy, but it has
already accomplished much. It has developed modern systems of
sanitation, has guided us in the building of hospitals, given
rules for the management of the sick-room which largely prevent
contagion from patient to nurse; it has told us what diseases are
contagious, and in what way; it has told us what sources of
contagion should be suspected and guarded against, and has thus
done very much to prevent the spread of disease. Its value is seen
in the fact that there has been a constant decrease in the death
rate since modern ideas of sanitation began to have any influence,
and in the fact that our general epidemics are less severe than in
former years, as well as in the fact that more people escape the
diseases which were in former times almost universal.
The study of preventive medicine takes into view several factors,
all connected with the method and means of contagion. They are the
following:
The Source of Infectious Material.--t has been learned that for
most diseases the infectious material comes from individuals
suffering with the disease, and that except in a few cases, like
malaria, we must always look to individuals suffering from disease
for all sources of contagion. It is found that pathogenic bacteria
are in all these cases eliminated from the patient in some way,
either from the alimentary canal or from skin secretions or
otherwise, and that any nurse with common sense can have no
difficulty in determining in what way the infectious material is
eliminated from her patients. When this fact is known and taken
into consideration it is a comparatively easy matter to devise
valuable precautions against distribution of such material. It is
thus of no small importance to remember that the simple presence
of bacteria in food or drink is of no significance unless these
bacteria have come from some source of disease infection.
The Method of Distribution.--The bacteria must next get from the
original source of the disease to the new susceptible individual.
Bacteria have no independent powers of distribution unless they be
immersed in liquids, and therefore their passage from individual
to individual must be a passive one. They are readily
transferred, however, by a number of different means, and the
study of these means is aiding much in checking contagion Study
along this line has shown that the means by which bacteria are
carried are several. First we may notice food as a distributor.
Food may become contaminated by infectious material in many ways;
for example, by contact with sewage, or with polluted water, or
even with eating utensils which have been used by patients. Water
is also likely to be contaminated with infectious material, and is
a fertile source for distributing typhoid and cholera. Milk may
become contaminated in a variety of ways, and be a source of
distributing the bacteria which produce typhoid fever,
tuberculosis, diphtheria, scarlet fever, and a few other less
common diseases. Again, infected clothing, bedding, or eating
utensils may be taken from a patient and be used by another
individual without proper cleansing. Direct contact, or contact
with infected animals, furnishes another method. Insects sometimes
carry the bacteria from person to person, and in some diseases
(tuberculosis, and perhaps scarlet fever and smallpox) we must
look to the air as a distributor of the infectious material.
Knowledge of these facts is helping to account for multitudes of
mysterious cases of infection, especially when we combine them
with the known sources of contagious matter.
Means of Invasion.--Bacteriology has shown us that different
species of parasitic bacteria have different means of entering the
body, and that each must enter the proper place in order to get a
foothold. After we learn that typhoid infectious material must
enter the mouth in order to produce the disease; that tuberculosis
may find entrance through the nose in breathing, while types of
blood poisoning enter only through wounds or broken skin, we learn
at once fundamental facts as to the proper methods of meeting
these dangers. We learn that with some diseases care exercised to
prevent the swallowing of infectious material is sufficient to
prevent contagion, while with others this is entirely
insufficient. When all these facts are understood it is almost
always perfectly possible to avoid contagion; and as these facts
become more and more widely known direct contagion is sure to
become less frequent.
Above all, it is telling us what becomes of the pathogenic
bacteria after being eliminated from the body of the patient; how
they may exist for a long time still active; how they may lurk in
filth or water dormant but alive, or how they may even multiply
there. Preventive medicine is telling us how to destroy those thus
lying in wait for a chance of infection, by discovering
disinfectants and telling us especially where and when to use
them. It has already taught us how to crush out certain forms of
epidemics by the proper means of destroying bacteria, and is
lessening the dangers from contagious diseases. In short, the
study of bacteriology has brought us into a condition where we are
no longer helpless in the presence of a raging epidemic. We no
longer sit in helpless dismay, as did our ancestors, when an
epidemic enters a community, but, knowing their causes and
sources, set about at once to remove them. As a result, severe
epidemics are becoming comparatively short-lived.
BACTERIA IN SURGERY.
In no line of preventive medicine has bacteriology been of so much
value and so striking in its results as in surgery. Ever since
surgery has been practised surgeons have had two difficulties to
contend with. The first has been the shock resulting from the
operation. This is dependent upon the extent of the operation, and
must always be a part of a surgical operation. The second has been
secondary effects following the operation. After the operation,
even though it was successful, there were almost sure to arise
secondary complications known as surgical fever, inflammation,
blood poisoning, gangrene, etc., which frequently resulted
fatally. These secondary complications were commonly much more
serious than the shock of the operation, and it used to be the
common occurrence for the patient to recover entirely from the
shock, but yield to the fevers which followed. They appeared to be
entirely unavoidable, and were indeed regarded as necessary parts
of the healing of the wound. Too frequently it appeared that the
greater the care taken with the patient the more likely he was to
suffer from some of these troubles. The soldier who was treated on
the battlefield and nursed in an improvised field hospital would
frequently recover, while the soldier who had the fortune to be
taken into the regular hospital, where greater care was possible,
succumbed to hospital gangrene. All these facts were clearly
recognised, but the surgeon, through ignorance of their cause, was
helpless in the presence of these inflammatory troubles, and felt
it always necessary to take them into consideration.
The demonstration that putrefaction and decay were caused by
bacteria, and the early proof that the silkworm disease was
produced by a micro-organism, led to the suggestion that the
inflammatory diseases accompanying wounds were similarly caused.
There are many striking similarities between these troubles and
putrefaction, and the suggestion was an obvious one. At first,
however, and for quite a number of years, it was impossible to
demonstrate the theory by finding the distinct species of micro-
organisms which produced the troubles. We have already seen that
there are several different species of bacteria which are
associated with this general class of diseases, but that no
specific one has any particular relation to a definite type of
inflammation. This fact made discoveries in this connection a slow
matter from the microscopical standpoint. But long before this
demonstration was finally reached the theory had received
practical application in the form of what has developed into
antiseptic or aseptic surgery.
Antiseptic surgery is based simply upon the attempt to prevent the
entrance of bacteria into the surgical wound. It is assumed that
if these organisms are kept from the wound the healing will take
place without the secondary fevers and inflammations which occur
if they do get a chance to grow in the wound. The theory met with
decided opposition at first, but accumulating facts demonstrated
its value, and to-day its methods have been adopted everywhere in
the civilized world. As the evidence has been accumulating,
surgeons have learned many important facts, foremost among which
is a knowledge of the common sources from which the infection of
wounds occurs. At first it was thought that the air was the great
source of infection, but the air bacteria have been found to be
usually harmless. It has appeared that the more common sources are
the surgeon's instruments, or his hands, or the clothing or
sponges which are allowed to come in contact with the wounds. It
has also appeared that the bacteria which produce this class of
troubles are common species, existing everywhere and universally
present around the body, clinging to the clothing or skin, and
always on hand to enter the wound if occasion offers. They are
always present, but commonly harmless. They are not foreign
invaders like the more violent pathogenic species, such as those
of Asiatic cholera, but may be compared to domestic enemies at
hand. It is these ever-present bacteria which the surgeon must
guard against. The methods by which he does this need not detain
us here. They consist essentially in bacteriological cleanliness.
The operation is performed with sterilized instruments under most
exacting conditions of cleanliness.
The result has been a complete revolution in surgery. As the
methods have become better understood and more thoroughly adopted,
the instances of secondary troubles following surgical wounds have
become less and less frequent until they have practically
disappeared in all simple cases. To-day the surgeon recognises
that when inflammatory troubles of this sort follow simple
surgical wounds it is a testimony to his carelessness. The skilful
surgeon has learned that with the precautions which he is able to
take to-day he has to fear only the direct effect of the shock of
the wound and its subsequent direct influence; but secondary
surgical fevers, blood poisoning, and surgical gangrene need not
be taken into consideration at all. Indeed, the modern surgeon
hardly knows what surgical gangrene is, and bacteriologists have
had practically no chance to study it. Secondary infections have
largely disappeared, and the surgeon is concerned simply with the
effect of the wound itself, and the power of the body to withstand
the shock and subsequently heal the wound.
With these secondary troubles no longer to disturb him, the
surgeon has become more and more bold. Operations formerly not
dreamed of are now performed without hesitation. In former years
an operation which opened the abdominal cavity was not thought
possible, or at least it was so nearly certain to result fatally
that it was resorted to only on the last extremity; while to-day
such operations are hardly regarded as serious. Even brain surgery
is becoming more and more common. Possibly our surgeons are
passing too far to the other extreme, and, feeling their power of
performing so many operations without inconvenience or danger,
they are using the knife in cases where it would be better to
leave Nature to herself for her own healing. But, be this as it
may, it is impossible to estimate the amount of suffering
prevented and the number of lives saved by the mastery of the
secondary inflammatory troubles which used to follow surgical
wounds.
Preventive medicine, then, has for its object the prevention
rather than the cure of disease. By showing the causes of disease
and telling us where and how they are contracted, it is telling us
how they may to a large extent be avoided. Unlike practical
medicine, this subject is one which has a direct relation to the
general public. While it may be best that the knowledge of
curative methods be confined largely to the medical profession, it
is eminently desirable that a knowledge of all the facts bearing
upon preventive medicine should be distributed as widely as
possible. One person can not satisfactorily apply his knowledge of
preventive medicine, if his neighbour is ignorant of or careless
of the facts. We can not hope to achieve the possibilities lying
along this line until there is a very wide distribution of
knowledge. Every epidemic that sweeps through our communities is a
testimony to the crying need of education in regard to such simple
facts as the source of infectious material, the methods of its
distribution, and the means of rendering it harmless.
PREVENTION IN INOCULATION.
It has long been recognised that in most cases recovery from one
attack of a contagious disease renders an individual more or less
immune against a second attack. It is unusual for an individual to
have the same contagious disease twice. This belief is certainly
based upon fact, although the immunity thus acquired is subject to
wide variations. There are some diseases in which there is little
reason for thinking that any immunity is acquired, as in the case
of tuberculosis, while there are others in which the immunity is
very great and very lasting, as in the case of scarlet fever.
Moreover, the immunity differs with individuals. While some
persons appear to acquire a lasting immunity by recovery from a
single attack, others will yield to a second attack very readily.
But in spite of this the fact of such acquired immunity is beyond
question. Apparently all infectious diseases from which a real
recovery takes place are followed by a certain amount of
protection from a second attack; but with some diseases the
immunity is very fleeting, while with others it is more lasting.
Diseases which produce a general infection of the whole system
are, as a rule, more likely to give rise to a lasting immunity
than those which affect only small parts. Tuberculosis, which, as
already noticed, is commonly quite localized in the body, has
little power of conveying immunity, while a disease like scarlet
fever, which affects the whole system, conveys a more lasting
protection.
Such immunity has long been known, and in the earlier years was
sometimes voluntarily acquired; even to-day we find some
individuals making use of the principle. It appears that a mild
attack of such diseases produces immunity equally well with a
severe attack, and acting upon this fact mothers have not
infrequently intentionally exposed their children to certain
diseases at seasons when they are mild, in order to have the
disease "over with" and their children protected in the future.
Even the more severe diseases have at times been thus voluntarily
acquired. In China it has sometimes been the custom thus to
acquire smallpox. Such methods are decidedly heroic, and of course
to be heartily condemned. But the principle that a mild type of
the disease conveys protection has been made use of in a more
logical and defensible way.
The first instance of this principle was in vaccination against
smallpox, now practised for more than a century. Cowpox is
doubtless closely related to smallpox, and an attack of the former
conveys a certain amount of protection against the latter. It was
easy, therefore, to inoculate man with some of the infectious
material from cowpox, and thus give him some protection against
the more serious smallpox. This was a purely empirical discovery,
and vaccination was practised long before the principle underlying
it was understood, and long before the germ nature of disease was
recognised. The principle was revived again, however, by Pasteur,
and this time with a logical thought as to its value. While
working upon anthrax among animals, he learned that here, as in
other diseases, recovery, when it occurred, conveyed immunity.
This led him to ask if it were not possible to devise a method of
giving to animals a mild form of the disease and thus protect them
from the more severe type. The problem of giving a mild type of
this extraordinarily severe disease was not an easy one. It could
not be done, of course, by inoculating the animals with a small
number of the bacteria, for their power of multiplication would
soon make them indefinitely numerous. It was necessary in some way
to diminish their violence. Pasteur succeeded in doing this by
causing them to grow in culture fluids for a time at a high
temperature. This treatment diminished their violence so much that
they could be inoculated into cattle, where they produced only the
mildest type of indisposition, from which the animals speedily
recovered. But even this mild type of the disease was triumphantly
demonstrated to protect the animals from the most severe form of
anthrax. The discovery was naturally hailed as a most remarkable
one, and one which promised great things in the future. If it was
thus possible, by direct laboratory methods, to find a means of
inoculating against a serious disease like anthrax, why could not
the same principle be applied to human diseases? The enthusiasts
began at once to look forward to a time when all diseases should
be thus conquered.
But the principle has not borne the fruit at first expected. There
is little doubt that it might be applied to quite a number of
human diseases if a serious attempt should be made. But several
objections arise against its wide application. In the first place,
the inoculation thus necessary is really a serious matter. Even
vaccination, as is well known, sometimes, through faulty methods,
results fatally, and it is a very serious thing to experiment upon
human beings with anything so powerful for ill as pathogenic
bacteria. The seriousness of the disease smallpox, its
extraordinary contagiousness, and the comparatively mild results
of vaccination, have made us willing to undergo vaccination at
times of epidemics to avoid the somewhat great probability of
taking the disease. But mankind is unwilling to undergo such an
operation, even though mild, for the purpose of avoiding other
less severe diseases, or diseases which are less likely to be
taken. We are unwilling to be inoculated against mild diseases, or
against the more severe ones which are uncommon. For instance, a
method has been devised for rendering animals immune against
lockjaw, which would probably apply equally well to man. But
mankind in general will never adopt it, since the danger from
lockjaw is so small. Inoculation must then be reserved for
diseases which are so severe and so common, or which occur in
periodical epidemics of so great severity, as to make people in
general willing to submit to inoculation as a protection. A
further objection arises from the fact that the immunity acquired
is not necessarily lasting. The cattle inoculated against anthrax
retain their protective powers for only a few months. How long
similar immunity might be retained in other cases we can not say,
but plainly this fact would effectually prevent this method of
protecting mankind from being used except in special cases. It is
out of the question to think of constant and repeated inoculations
against various diseases.
As a result, the principle of inoculation as an aid in preventive
medicine has not proved of very much value. The only other human
disease in which it has been attempted seriously is Asiatic
cholera. This disease in times of epidemics is so severe and the
chance of infection is so great as to justify such inoculation.
Several bacteriologists have in the last few years been trying to
discover a harmless method of inoculating against this disease.
Apparently they have succeeded, for experiments in India, the home
of the cholera, have been as successful as could be anticipated.
Bacteriological science has now in its possession a means of
inoculation against cholera which is perhaps as efficacious as
vaccination is against smallpox. Whether it will ever be used to
any extent is doubtful, since, as already pointed out, we are in a
position to avoid cholera epidemics by other means. If we can
protect our communities by guarding the water supply, it is not
likely that the method of inoculation will ever be widely used.
Another instance of the application of preventive inoculation has
been made, but one based upon a different principle. Hydrophobia
is certainly one of the most horrible of diseases, although
comparatively rare. Its rarity would effectually prevent mankind
from submitting to a general inoculation against it, but its
severity would make one who had been exposed to it by the bite of
a rabid animal ready to submit to almost any treatment that
promised to ward off the disease. In the attempt to discover a
means of inoculating against this disease it was necessary,
therefore, to find a method that could be applied after the time
of exposure--i.e., after the individual had been bitten by the
rabid animal. Fortunately, the disease has a long period of
incubation, and one that has proved long enough for the purpose. A
method of inoculation against this disease has been devised by
Pasteur, which can be applied after the individual has been bitten
by the rabid animal. Apparently, however, this preventive
inoculation is dependent upon a different principle from
vaccination or inoculation against anthrax. It does not appear to
give rise to a mild form of the disease, thus protecting the
individual, but rather to an acquired tolerance of the chemical
poisons produced by the disease. It is a well-known physiological
fact that the body can become accustomed to tolerate poisons if
inured to them by successively larger and larger doses. It is by
this power, apparently, that the inoculation against hydrophobia
produces its effect. Material containing the hydrophobia poison
(taken from the spinal cord of a rabbit dead with the disease) is
injected into the individual after he has been bitten by a rabid
animal. The poisonous material in the first injection is very
weak, but is followed later by a more powerful inoculation. The
result is that after a short time the individual has acquired the
power of resisting the hydrophobia poisons. Before the incubation
period of the original infectious matter from the bite of the
rabid animal has passed, the inoculated individual has so
thoroughly acquired a tolerance of the poison that he successfully
resists the attack of the infection. This method of inoculation
thus neutralizes the effects of the disease by anticipating them.
The method of treatment of hydrophobia met with extraordinarily
violent opposition. For several years it was regarded as a
mistake. But the constantly accumulating statistics from the
Pasteur Institute have been so overwhelmingly on one side as to
quiet opposition and bring about a general conviction that the
method is a success.
The method of preventive inoculation has not been extensively
applied to human diseases in addition to those mentioned. In a few
cases a similar method has been used to guard against diphtheria.
Among animals, experiment has shown that such methods can quite
easily be obtained, and doubtless the same would be true of
mankind if it was thought practical or feasible to apply them.
But, for reasons mentioned, this feature of preventive medicine
will always remain rather unimportant, and will be confined to a
few of the more violent diseases.
It may be well to raise the question as to why a single attack
with recovery conveys immunity. This question is really a part of
the one already discussed as to the method by which the body cures
disease. We have seen that this is in part due to the development
of chemical substances which either neutralize the poisons or act
as germicide upon the bacteria, or both, and perhaps due in part
to an active destruction of bacteria by cellular activity
(phagocytosis). There is little reason to doubt that it is the
same set of activities which renders the animal immune. The forces
which drive off the invading bacteria in one case are still
present to prevent a second attack of the same species of
bacterium. The length of time during which these forces are active
and sufficient to cope with any new invaders determines the length
of time during which the immunity lasts. Until, therefore, we can
answer with more exactness just how cure is brought about in case
of disease, we shall be unable to explain the method of immunity.
LIMITS OF PREVENTIVE MEDICINE.
With all the advance in preventive medicine we can not hope to
avoid disease entirely. We are discovering that the sources of
disease are on all sides of us, and so omnipresent that to avoid
them completely is impossible. If we were to apply to our lives
all the safeguards which bacteriology has taught us should be
applied in order to avoid the different diseases, we would
surround ourselves with conditions which would make life
intolerable. It would be oppressive enough for us to eat no food
except when it is hot, to drink no water except when boiled, and
to drink no milk except after sterilization; but these would not
satisfy the necessary conditions for avoiding disease. To meet all
dangers, we should handle nothing which has not been sterilized,
or should follow the handling by immediately sterilizing the
hands; we should wear only disinfected clothes, we should never
put our fingers in our mouths or touch our food with them; we
should cease to ride in public conveyances, and, indeed, should
cease to breathe common air. Absolute prevention of the chance of
infection is impossible. The most that preventive medicine can
hope for is to point out the most common and prolific sources of
infection, and thus enable civilized man to avoid some of his most
common troubles. It becomes a question, therefore, where we will
best draw the line in the employment of safeguards. Shall we drink
none except sterilized milk, and no water unless boiled? or shall
we put these occasional sources of danger in the same category
with bicycle and railroad accidents, dangers which can be avoided
by not using the bicycle or riding on the rail, but in regard to
which the remedy is too oppressive for application?
Indeed, when viewed in a broad philosophical light it may not be
the best course for mankind to shun all dangers. Strength in the
organism comes from the use rather than the disuse of our powers.
It is certain that the general health and vigour of mankind is to
be developed by meeting rather than by shunning dangers.
Resistance to disease means bodily vigour, and this is to be
developed in mankind by the application of the principle of
natural selection. In accordance with this principle, disease will
gradually remove the individuals of weak resisting powers, leaving
those of greater vigour. Parasitic bacteria are thus a means of
preventing the continued life of the weaker members of the
community, and so tend to strengthen mankind. By preventive
medicine many a weak individual who would otherwise succumb
earlier in the struggle is enabled to live a few years longer.
Whatever be our humanitarian feeling for the individual, we can
not fail to admit that this survival of the weak is of no benefit
to the race so far as the development of physical nature is
concerned. Indeed, if we were to take into consideration simply
the physical nature of man we should be obliged to recommend a
system such as the ancient Spartans developed, of exposing to
death all weakly individuals, that only the strong might live to
become the fathers of future generations. In this light, of
course, parasitic diseases would be an assistance rather than a
detriment to the human race. Of course such principles will never
again be dominant among men, and our conscience tells us to do all
we can to help the weak. We shall doubtless do all possible to
develop preventive medicine in order to guard the weak against
parasitic organisms. But it is at all events well for us to
remember that we can never hope to develop the strength of the
human race by shunning evil, but rather by combating it, and the
power of the human race to resist the invasions of these organisms
will never be developed by the line of action which guards us from
attack. Here, as in other directions, the principles of modern
humanity have, together with their undoubted favourable influence
upon mankind, certain tendencies toward weakness. While we shall
still do our utmost to develop preventive medicine in a proper
way, it may be well for us to remember these facts when we come to
the practical question of determining where to draw the limits of
the application of methods for preventing infectious diseases.
CURATIVE MEDICINE.
Bacteriology has hitherto contributed less to curative than to
preventive medicine. Nevertheless, its contributions to curative
medicine have not been unimportant, and there is promise of much
more in the future. It is, of course, unsafe to make predictions
for the future, but the accomplishments of the last few years give
much hope as to further results.
DRUGS.
It was at first thought that a knowledge of the specific bacteria
which cause a disease would give a ready means of finding specific
drugs for the cure of such disease. If a definite species of
bacterium causes a disease and we can cultivate the organism in
the laboratory, it is easy to find some drugs which will be fatal
to its growth, and these same drugs, it would seem, should be
valuable as medicines in these diseases. This hope has, however,
proved largely illusive. It is very easy to find some drug which
proves fatal to the specific germs while growing in the culture
media of the laboratory, but commonly these are of little or no
use when applied as medicines. In the first place, such substances
are usually very deadly poisons. Corrosive sublimate is a
substance which destroys all pathogenic germs with great rapidity,
but it is a deadly poison, and can not be used as a drug in
sufficient quantity to destroy the parasitic bacteria in the body
without at the same time producing poisonous effects on the body
itself. It is evident that for any drug to be of value in thus
destroying bacteria it must have some specially strong action upon
the bacteria. Its germicide action on the bacteria should be so
strong that a dose which would be fatal or very injurious to them
would be too small to have a deleterious influence on the body of
the individual. It has not proved an easy task to discover drugs
which will have any value as germicides when used in quantities so
small as to produce no injurious effect on the body.
A second difficulty is in getting the drug to produce its effect
at the right point. A few diseases, as we have noticed, are
produced by bacteria which distribute themselves almost
indiscriminately over the body; but the majority are somewhat
definitely localized in special points. Tuberculosis may attack a
single gland or a single lobe of the lung. Typhoid germ is
localized in the intestines, liver, spleen, etc. Even if it were
possible to find some drug which would have a very specific effect
upon the tuberculosis bacillus, it is plain that it would be a
very questionable method of procedure to introduce this into the
whole system simply that it might have an effect upon a very small
isolated gland. Sometimes such a bacterial affection may be
localized in places where it can be specially treated, as in the
case of an attack on a dermal gland, and in these cases some of
the germicides have proved to be of much value. Indeed, the use of
various disinfectants connected with abscesses and superficial
infections has proved of much value. To this extent, in
disinfecting wounds and as a local application, the development of
our knowledge of disinfectants has given no little aid to curative
medicine.
Very little success, however, has resulted in the attempt to find
specific drugs for specific diseases, and it is at least doubtful
whether many such will ever be found. The nearest approach to it
is quinine as a specific poison for malarial troubles. Malarious
diseases are not, however, produced by bacteria but by a
microscopic organism of a very different nature, thought to be an
animal rather than a plant. Besides this there has been little or
no success in discovering specifics in the form of drugs which can
be given as medicines or inoculated with the hope of destroying
special kinds of pathogenic bacteria without injury to the body.
While it is unwise to make predictions as to future discoveries,
there seems at present little hope for a development of curative
medicine along these lines.
VIS MEDICATRIX NATURAE.
The study of bacterial diseases as they progress in the body has
emphasized above all things the fact that diseases are eventually
cured by a natural rather than by an artificial process. If a
pathogenic bacterium succeeds in passing the outer safeguards and
entering the body, and if it then succeeds in overcoming the
forces of resistance which we have already noticed, it will begin
to multiply and produce mischief. This multiplication now goes on
for a time unchecked, and there is little reason to expect that we
can ever do much toward checking it by means of drugs. But after a
little, conditions arise which are hostile to the further growth
of the parasite. These hostile conditions are produced perhaps in
part by the secretions from the bacteria, for bacteria are unable
to flourish in a medium containing much of their own secretions.
The secretions which they produce are poisons to them as well as
to the individual in which they grow, and after these have become
quite abundant the further growth of the bacterium is checked and
finally stopped. Partly, also, must we conclude that these hostile
conditions are produced by active vital powers in the body of the
individual attacked. The individual, as we have seen, in some
cases develops a quantity of some substance which neutralizes the
bacterial poisons and thus prevents their having their maximum
effect. Thus relieved from the direct effects of the poisons, the
resisting powers are recuperated and once more begin to produce a
direct destruction of the bacteria. Possibly the bacteria, being
now weakened by the presence of their own products of growth, more
readily yield to the resisting forces of the cell life of the
body. Possibly the resisting forces are decidedly increased by the
reactive effect of the bacteria and their poisons. But, at all
events, in cases where recovery from parasitic diseases occurs,
the revived powers of resistance finally overcome the bacteria,
destroy them or drive them off, and the body recovers.
All this is, of course, a natural process. The recovery from a
disease produced by the invasion of parasitic bacteria depends
upon whether the body can resist the bacterial poisons long enough
for the recuperation of its resisting powers. If these poisons are
very violent and produced rapidly, death will probably occur
before the resisting powers are strong enough to drive off the
bacteria. In the case of some diseases the poisons are so violent
that this practically always occurs, recovery being very
exceptional. The poison produced by the tetanus bacillus is of
this nature, and recovery from lockjaw is of the rarest
occurrence. But in many other diseases the body is able to
withstand the poison, and later to recover its resisting powers
sufficiently to drive off the invaders. In all cases, however, the
process is a natural one and dependent upon the vital activity of
the body. It is based at the foundation, doubtless, upon the
powers of the body cells, either the phagocytes or other active
cells. The body has, in short, its own forces for repelling
invasions, and upon these forces must we depend for the power to
produce recovery.
It is evident that all these facts give us very little
encouragement that we shall ever be able to cure diseases directly
by means of drugs to destroy bacteria, but, on the contrary, that
we must ever depend upon the resisting powers of the body. They
teach us, moreover, along what line we must look for the future
development of curative medicine. It is evident that scientific
medicine must turn its attention toward the strengthening and
stimulating of the resisting and curative forces of the body. It
must be the physician's aim to enable the body to resist the
poisons as well as possible and to stimulate it to re-enforce its
resistant forces. Drugs have a place in medicine, of course, but
this place is chiefly to stimulate the body to react against its
invading hosts. They are, as a rule, not specific against definite
diseases. We can not hope for much in the way of discovering
special medicines adapted to special diseases. We must simply look
upon them as means which the physician has in hand for stimulating
the natural forces of the body, and these may doubtless vary with
different individual natures. Recognising this, we can see also
the logic of the small dose as compared to the large dose. A small
dose of a drug may serve as a stimulant for the lagging forces,
while a larger dose would directly repress them or produce
injurious secondary effects. As soon as we recognise that the aim
of medicine is not to destroy the disease but rather to stimulate
the resisting forces of the body, the whole logic of therapeutics
assumes a new aspect.
Physicians have understood this, and, especially in recent years,
have guided their practice by it. If a moderate dose of quinine
will check malaria in a few days, it does not follow that twice
the dose will do it in half the time or with twice the certainty.
The larger doses of the past, intended to drive out the disease,
have been everywhere replaced by smaller doses designed to
stimulate the lagging body powers. The modern physician makes no
attempt to cure typhoid fever, having long since learned his
inability to do this, at least if the fever once gets a foothold;
but he turns his attention to every conceivable means of
increasing the body's strength to resist the typhoid poison,
confident that if he can thus enable the patient to resist the
poisoning effects of the typhotoxine his patient will in the end
react against the disease and drive off the invading bacteria. The
physician's duty is to watch and guard, but he must depend upon
the vital powers of his patient to carry on alone the actual
battle with the bacterial invaders.
ANTITOXINES.
In very recent times, however, our bacteriologists have been
pointing out to the world certain entirely new means of assisting
the body to fight its battles with bacterial diseases. As already
noticed, one of the primal forces in the recovery, from some
diseases, at least, is the development in the body of a substance
which acts as an antidote to the bacterial poison. So long as this
antitoxine is not present the poisons produced by the disease will
have their full effect to weaken the body and prevent the revival
of its resisting powers to drive off the bacteria. Plainly, if it
is possible to obtain this antitoxine in quantity and then
inoculate it into the body when the toxic poisons are present, we
have a means for decidedly assisting the body in its efforts to
drive off the parasites. Such an antidote to the bacterial poison
would not, indeed, produce a cure, but it would perhaps have the
effect of annulling the action of the poisons, and would thus give
the body a much greater chance to master the bacteria. It is upon
this principle that is based the use of antitoxines in diphtheria
and tetanus
It will be clear that to obtain the antitoxine we must depend upon
some natural method for its production. We do not know enough of
the chemical nature of the antitoxines to manufacture them
artificially. Of course we can not deny the possibility of their
artificial production, and certain very recent experiments
indicate that perhaps they may be made by the agency of
electricity. At present, however, we must use natural methods, and
the one commonly adopted is simple. Some animal is selected whose
blood is harmless to man and that is subject to the disease to be
treated. For diphtheria a horse is chosen. This animal is
inoculated with small quantities of the diphtheria poison without
the diphtheria bacillus. This poison is easily obtained by causing
the diphtheria bacillus to grow in common media in the laboratory
for a while, and the toxines develop in quantity; then, by proper
filtration, the bacteria themselves can be removed, leaving a pure
solution of the toxic poison. Small quantities of this poison are
inoculated into the horse at successive intervals. The effect on
the horse is the same as if the animal had the disease. Its cells
react and produce a considerable quantity of the antitoxine which
remains in solution in the blood of the animal. This is not
theory, but demonstrated fact. The blood of a horse so treated is
found to have the effect of neutralizing the diphtheria poison,
although the blood of the horse before such treatment has no such
effect. Thus there is developed in the horse's blood a quantity of
the antitoxine, and now it may be used by physicians where needed.
If some of this horse's blood, properly treated, be inoculated
into the body of a person who is suffering from diphtheria, its
effect, provided the theory of antitoxines is true, will be to
counteract in part, at least, the poisons which are being produced
in the patient by the diphtheria bacillus. This does not cure the
disease nor in itself drive off the bacilli, but it does protect
the body from the poisons to such an extent as to enable it more
readily to assert its own resisting powers.
This method of using antitoxines as a help in curing disease is
very recent, and we can not even guess what may come of it. It has
apparently been successfully applied in diphtheria. It has also
been used in tetanus with slight success. The same principle has
been used in obtaining an antidote for the poison of snake bites,
since it has appeared that in this kind of poisoning the body will
develop an antidote to the poison if it gets a chance. Horses have
been treated in the same way as with the diphtheria poison, and in
the same way they develop a substance which neutralizes the snake
poison. Other diseases are being studied to-day with the hope of
similar results. How much further the principle will go we can not
say, nor can we be very confident that the same principle will
apply very widely. The parasitic diseases are so different in
nature that we can hardly expect that a method which is
satisfactory in meeting one of the diseases will be very likely to
be adapted to another. Vaccination has proved of value in
smallpox, but is not of use in other human diseases. Inoculation
with weakened germs has proved of value in anthrax and fowl
cholera, but will not apply to all diseases. Each of these
parasites must be fought by special methods, and we must not
expect that a method that is of value in one case must necessarily
be of use elsewhere. Above all, we must remember that the
antitoxines do not cure in themselves; they only guard the body
from the weakening effects of the poisons until it can cure
itself, and, unless the body has resisting powers, the antitoxine
will fail to produce the desired results.
One further point in the action of the antitoxines must be
noticed. As we have seen, a recovery from an attack of most germ
diseases renders the individual for a time immune against a second
attack. This applies less, however, to a recovery after the
artificial inoculation with antitoxine than when the individual
recovers without such aid. If the individual recovers quite
independently of the artificial antitoxine, he does so in part
because he has developed the antitoxines for counteracting the
poison by his own powers. His cellular activities have, in other
words, been for a moment at least turned in the direction of
production of antitoxines. It is to be expected, therefore, that
after the recovery they will still have this power, and so long as
they possess it the individual will have protection from a second
attack. When, however, the recovery results from the artificial
inoculation of antitoxine the body cells have not actively
produced antitoxine. The neutralization of the poisons has been a
passive one, and after recovery the body cells are no more engaged
in producing antitoxine than before. The antitoxine which was
inoculated is soon eliminated by secretion, and the body is left
with practically the same liability to attack as before. Its
immunity is decidedly fleeting, since it was dependent not upon
any activity on the part of the body, but upon an artificial
inoculation of a material which is rapidly eliminated by
secretion.
CONCLUSION.
It is hoped that the outline which has been given of the bacterial
life of Nature may serve to give some adequate idea of these
organisms and correct the erroneous impressions in regard to them
which are widely prevalent. It will be seen that, as our friends,
bacteria play a vastly more important part in Nature than they do
as our enemies. These plants are minute and extraordinarily
simple, but, nevertheless, there exists a large number of
different species. The number of described forms already runs far
into the hundreds, and we do not yet appear to be approaching the
end of them. They are everywhere in Nature, and their numbers are
vast beyond conception. Their powers of multiplication are
inconceivable, and their ability to produce profound chemical
changes is therefore unlimited. This vast host of living beings
thus constitutes a force or series of forces of tremendous
significance. Most of the vast multitude we must regard as our
friends. Upon them the farmer is dependent for the fertility of
his soil and the possibility of continued life in his crops. Upon
them the dairyman is dependent for his flavours. Upon them
important fermentative industries are dependent, and their
universal powers come into action upon a commercial scale in many
a place where we have little thought of them in past years. We
must look upon them as agents ever at work, by means of which the
surface of Nature is enabled to remain fresh and green. Their
power is fundamental, and their activities are necessary for the
continuance of life. A small number of the vast host, a score or
two of species, unfortunately for us, find their most favourable
living place in the human body, and thus become human parasites.
By their growth they develop poisons and produce disease. This
small class of parasites are then decidedly our enemies. But,
taken all together, we must regard the bacteria as friends and
allies. Without them we should not have our epidemics, but without
them we should not exist. Without them it might be that some
individuals would live a little longer, if indeed we could live at
all. It is true that bacteria, by producing disease, once in a
while cause the premature death of an individual; once in a while,
indeed, they may sweep off a hundred or a thousand individuals;
but it is equally true that without them plant and animal life
would be impossible on the face of the earth.