Popular Science Monthly/Volume 37/October 1890/Invisible Assailants of Health
|INVISIBLE ASSAILANTS OF HEALTH.|
By SAMUEL HART, M. D.
IN the natural competitive strife for existence among all organic beings, man had formerly recognized the fact that he was in direct antagonism with opponents which were formidable in proportion to their size, strength, and ferocity; and against whose aggressions he was to measure force, guided by his best intelligence. It has been, of course, a matter of common observation from most primitive times that some mysterious, invisible influence was constantly at war upon human life, but whose nature and intent were believed to be beyond permissible human ken. Scarcely a ray of light seems to have been shed upon this occult cause of human destruction until the present century; indeed, until within the last score of years. It is true, microscopy had been gradually unveiling to our astonished vision a new world, teeming with life of incalculable activity and scientific importance. But only recently have improved instruments and methods transformed a former invisible field into a true vivarium of beings, each having its distinctive size, color, form, requirement for food and place, with its cycle of birth, life, and death peculiar to its species.
It is now understood that our material world, with its visible occupants, is supplemented by and interdependent with myriads of micro-organisms, permeating or enveloping all matter, and whose relation to organic life is essentially cosmical. In some of their multifarious forms they are the direct and only means and medium of transformation of material from its cruder form into the appropriate food for all organic beings; apparently having the power of wresting atom from atom in the mineral world in order to render it available for themselves as well as for plants and animals; thus performing a work purely beneficent and essential. Other forms of minute organisms are employed in the mutations of nature in undoing the work of the former; and, as if endowed with a spirit of maleficence, are occupied solely with the work of decomposing all organic substances, inducing decay and death.
These bodies are of the so-called low forms of life; impelled by natural necessities to provide for themselves where and as best they may. They are of independent vitality, each individual having its definite organization and requirement as to kind of food, temperature, and amount of light and air. They belong to distinct species, and are reproduced in kind, with as much exactitude in size and form as are the large plants and animals, both of which natural divisions they represent.
They increase with such amazing rapidity that, unless limited by want of nutriment and favorable environment, a single species would in a few years occupy the earth's surface to the exclusion of all other life.
Many species are of wonderful vitality and tenacity of life, and resist the extremes of temperature, of boiling and freezing. Others may be dried to an entire suspension of vitality for months and years; wafted here and there by the winds until, under favoring circumstances, they renew their wonted activity. Scattered on the snow of the hill-side, and carried down with the spring freshet, miles away, they may be swallowed with the water by some unfortunate individual, and perhaps prove their presence and their source by inducing in him an infectious disease of their specific kind.
The microbes may be captured, and cultivated on beds of gelatin, albumen, sugar, and in broth of meats; and under skillful management be made to furnish flourishing colonies and specimens of the highest degree of development. Or they may be starved and chilled to such helpless weakness and attenuation as to seem to lose their specific characteristics. Those we are considering are among the most minute bodies within the possible scope of microscopy. This, and their perfect transparency, have heretofore seemed an insurmountable hindrance to our further knowledge of them. But the discovery of their strong affinity for certain of the intense coloring matters has been fortunate and timely, furnishing a key to brilliant developments, since it is found that certain species show a predilection for special colors; and a particular part of the microbe, as its membrane, or its contents, may unite with the color, while other parts may totally reject it—thus giving, not only outlines, but illuminated internal structure, otherwise invisible and unknown.
The extreme minuteness, then, of these bodies has heretofore been the bar and hindrance to our better knowledge of them. But already we have been able to peer downward and inward, from gross visible matter, through organs, tissues, cells, nuclei, nucleoli, and granules, until, in the so-called structureless protoplasm, our present hunting-ground and limit, we seem to have reached the confines of the inorganic molecule and atom, which are subject to chemical instead of physiological law. The modern discoveries in this microcosmic realm, and the demonstration of the causative relation of micro-organisms to disease, upon which the "germ theory of disease" depends, stands so conspicuously as a scientific success, and is a step so important toward the alleviation of suffering, the prolongation of life, and enhancement of human happiness as to be the subject of universal congratulation.
In order to comprehend the importance of this subject, it must be assumed that each of the long list of diseases known as infectious is caused by its own specific virus, and that no other material or combination of agencies can produce it. This fact is universally recognized. Furthermore, it has been demonstrated in a large proportion of these diseases that the essential principle of infection in the virus is the living germ called the pathogenic microbe.
The literally vital relation of microbic to human life can be observed in the following general statement: The pathogenic microbes cause four fifths of all diseases of the human family; they destroy more lives than war, famine, fire, murders, shipwreck, and all other casualties; and they actually abbreviate the average natural term of human life by three fourths, and constantly depress the health average of the world's population far below its natural standard.
They are an insidious but powerful and relentless enemy to human kind, holding sway over a large part of the most beautiful and fertile portions of the earth, excluding man at the peril of his life; while, as if with malicious discrimination, ferocious animals and venomous reptiles find there their congenial home, and vegetation reaches its acme of luxuriance. Like some diabolical spirit, in the form of the epidemic, it leaves its native habitat, and with insatiate malignity, sometimes with slow but irresistible progress, and again by rapid flight, passes all barriers of mountain, sea, and distance in its pursuit of man, its only known object, and whose destruction is its only visible effect. This is shown in Asiatic cholera, the plague, yellow fever, and the lesser scourges. The strife for possession in some coveted regions has been progressing for ages. Man may advance his outposts under the favoring light of sunshine, but must retreat, or fortify himself against the dangerous shades of night, until, by slow degrees, advantages are gained over the invisible enemy.
The Italian Pontine marshes, the jungles of India, the banks and shores of the tropics, our own Southern lowlands and fertile, new prairies are the strongholds of Bacillus malarial.
"The pestilence that walketh in darkness, and the sickness that wasteth at noonday," are known to be the work of the armies of the microbes.
Some of the means and methods of the micrologist, in his researches, must be mentioned. His outfit is extensive and novel. It includes the best known microscopes and a well-constructed incubator with heater and thermometer, numerous test-glasses, beakers, filters, acids, alkalies, deep-colored dyes, and a good supply of prepared cotton.
In studying the life history of his microbes he will require a well-supplied commissariat. He must be a professional caterer and a bountiful feeder. He must have fluids, semi-fluids, and solids, broths of various meats, peptonized food, the serum of blood, à la Koch, and Pasteur's favorite recipe with the French refinement: Recipe, 100 parts distilled water, 10 parts pure cane sugar, 1 part tartrate of ammonium, and the ash of 1 part of yeast. Among the substantial must be found, boiled white of egg, starch, gelatin, Japan isinglass, and potato—the last, from South as well as North America.
The appointments of his cuisine, and the extreme care and delicacy of manipulation required, will be shown in the preparation of a broth for the cultivation of a particular species of microbe. First, let it be remembered, all our surroundings are swarming with micro-organisms, a thousand times more numerous than the locusts of Egypt, and to exclude them from the kneading-troughs of the micrologist requires all the knowledge of the last quarter of the nineteenth century. A matter of the first importance, then, is that everything connected with the cultivation of microbes must be sterilized; which means that every microbe not wanted for observation must be destroyed; and no exorcism except by fire or the strongest antiseptics is found available. The preparation of a nutrient material for the cultivation of selected germs, according to Klein, will illustrate:
Place in a glass beaker fresh meat and water, equal weights; boil one hour; strain through a sterilized filter; after allowing the bouillon to stand for five hours, boil and filter as before. When cool, place in preserving glasses which have been sterilized by the flame of gas or the hot oven; then close by sterilized cotton, and boil again for over thirty minutes, and cover the mouth of the glass with an inverted beaker, one half filled with sterilized cotton, in order to effectually exclude the germ-laden air. Boil again the next day, and, when cool, place in an incubator for twenty-four hours at a suitable warmth, in order to hatch into life some possible germ of salamander endurance; and, finally, boil again for more than thirty minutes, in order to destroy this last suspected germ. If everything has been skillfully done, we have now a culture fluid exactly suited to the growth and development of a certain kind of germ only. These numerous steps and precautions for food-making may appear useless and absurd, but a little haste or a false step would undo the work of many days, and only this extraordinary attention to every detail has, after years of investigation, attended with acrimonious discussion among scientists, finally and forever settled the question of "spontaneous generation," as if in reassertion of the law that every living thing shall bring forth after its kind.
The method of demonstrating the germ cause of disease is as follows: Using only sterilized test-tubes, forceps, pipettes, cotton, etc., take a particle of virus, known or supposed to contain pathogenic microbes, from a person suffering from an infectious disease, insert it by a delicate glass pipette through, the sterilized cotton plug of a test-tube containing some of the prepared culture material, and deposit it there. Then place the tube in an incubator, warmed to the required degree, and let it remain for the number of hours suited to the peculiar requirement of its germ contents. By this means a vigorous progeny of one kind of microbe is obtained, while the tendency is to eliminate other kinds whose requirements are different.
But to further insure the. exclusion of the ubiquitous horde, take out carefully a little colony of the vigorous microbes of the first culture through the cotton covering and place it in a new culture-tube with the same precautions as before, and so on, until, through high feeding of our test microbes and the adverse treatment of the others, we have, by microscopic tests, the thoroughbred, vigorous, and, may be, deadly microbe, which may be seen and every characteristic noted as to size, form, coloring, manner and time of development, all of which enable the observer to fix its classification. But the crucial test as to the relationship of a certain species of microbe to a particular disease is made as follows: Take, as above, the microbes from an individual suffering from a well-known infectious disease, cultivate them to complete isolation and perfection, and introduce them by inoculation into the blood or tissues of a healthy person. Here they must undergo a period of development or incubation, requiring just the number of days and hours as in the culture-tube. This fully developed disease must be strictly the same as that which furnished the test germs.
In making these experiments with the virus of dangerous diseases the human subject can not, of course, be deliberately employed; but casual inoculations and infections furnish opportunities for exact observation. A few enthusiastic pathologists and would-be martyrs have submitted to inoculations which have proved of scientific value. The inferior animals furnish much valuable material in this line, although they are entirely exempt from many diseases belonging to man; while in the human subject there seems a greater general susceptibility to microbic infection.
Founded upon the knowledge of the natural history of the pathogenic microbes has come the only scientific and satisfactory classification of the infectious diseases. It may be stated, as a rule, that the virus of infectious diseases originates either in the bodies of diseased living beings or in decomposing organic matter. When the germs of the virus mature in the living being, ready for reproduction in another person, they produce the acute contagious diseases, including small-pox, chicken-pox, scarlet fever, typhns fever, relapsing fever; measles, miliary fever, influenza, whooping-cough, and hydrophobia.
In another class, called miasmatic contagions, the germs are propagated in diseased persons, but, as a law of their further development, they must undergo one stage of change outside of the body, in some decomposing organic matter, before they can again produce their peculiar disease in a healthy person, except by inoculation. To these miasmatic contagious diseases belong typhoid fever, yellow fever, cholera, diphtheria, acute consumption, cerebro-spinal meningitis, and erysipelas. When the virus originates entirely in decomposing vegetable matter, we have the malarious diseases: intermittent fever, remittent fever, continued malarial fever, pernicious fever, dengue fever, and chronic malarial infection.
Adopting this classification gives practical advantages without waiting for the demonstration of the particular microbes of each disease or their modus operandi. It is sufficient practically to know that the whole list of infectious diseases is accounted for under well-known laws of microbic generation. Indeed, the pathogenic cause may simply be called a virus; reserving only a distinctive character for each of the classes mentioned, viz.:
1. A virus which reaches full development in the diseased person, ready for infection in another, as in the small-pox class.
2. A virus which must be produced in the diseased person, but is not transmissible to another until after undergoing further development outside of the body; and usually in some decomposing organic matter. This is true of the typhoid-fever class.
3. Where the virus originates invariably in decomposing organic matter, and, after infecting the human subject, is never transmissible directly from one individual to another. This is the malarial class, including all the intermittent fevers, or the agues of slight degree as well as dangerous remittents and pernicious fevers, the intermittent neuralgias, and the "dumb agues."
Numerous other and very extensively prevalent diseases are known to be of microbic origin; among them pneumonia, rheumatism, tetanus, rabies, and the venereal in its numerous forms and phases.
Aside from the advantage of a scientific classification of diseases is that gained in the matter of prevention as well as cure; in both of which much has already been realized.
The means and manner of action of microbes in their destruction of life and health are various, and in some instances, as yet, obscure. As a prerequisite to their infectious development they must gain access to the blood or tissues through the cutaneous exterior or the mucous interior of the body; each species having its peculiar site for ingress, its locality for operation, and its peculiar way of accomplishing the destructive work. Some produce harmful if not fatal changes in the blood by appropriating some of its vital qualities, leaving the system robbed and impoverished. Others seem to obstruct the minute vessels by their immense numbers, and thus do harm in a mechanical way. Some attack the blood-cells, penetrate their walls, and absorb their contents. Another and most important action of microbes is the production of poisons of deadly intensity, tending not only to the destruction of the infected person, but of themselves as well.
These products of the pathogenic germs, called ptomaines, seem to be the means of the suicidal limitation of germ-life in certain instances—where, having gained access to the healthy tissues, they nourish for a time, destroying as they go; but presently they lose their vitality, poisoned by their own venom, which may be sufficient in quantity and intensity to destroy the individual infected. This fortunate tendency to self-destruction of microbic life seems to belong to the infectious diseases.
A remarkable and important fact here is the exemption acquired by the individual once having a disease from all future attacks. The explanation is as yet difficult. By some pathologists it is supposed that the change in the system is due to the permanent retention of a sufficient amount of the ptomaines generated by the first microbic invasion to prevent a reintroduction of the same species. In that case the ptomaine would prove no hindrance to the successful attack of other species. Some suppose that an essential nutritive principle in the system becomes completely consumed by the first attack, and may never be reproduced to support a second one. But recent, observations on the behavior of certain cells furnish a means, at once the most plausible and remarkable, for explaining the acquired disease-immunity, as well as a variable degree of original protection. These cells, called leucocytes and phagocytes, seem possessed of an instinctive, independent existence and behavior, suggestive of intellection. They are capable of locomotion, and a change of size and form—being constructed of elastic cell-walls of most filmy attenuation.
Their purpose, in part at least, seems to be to protect the system from harm within the blood, organs, and tissues. They are found where they may render the most ready and efficient service, particularly in the blood and in the air-cells and bronchioles of the lungs. Like a light guard in peaceful times, they are not conspicuously numerous; but in time of an attack they present themselves in great numbers and efficiency, and their energy in defense seems increased by any opposition not quite overwhelming.
The means of aggression or defense, as well as of sustenance, of the phagocyte, is by attaching itself to a particle of matter, and gradually surrounding and incasing it in its membranous walls until it is literally swallowed. If the particle should be a microbe, rich in protoplasm, it would be digested by the voracious and omnivorous phagocyte; but if of mineral origin, as dust of coal or sand inhaled by the lungs, it would be carried to the surface or to a safe receptacle, where the cell, having performed its mission, deposits itself, still incasing its burden. The phagocytes seem to meet whole broods of infective microbes which may have invaded the body, and destroy them, and, as it were, gradually acquire and permanently retain such efficiency as in future invasions of the same species to prevent any harmful action. The contest between these opposing forces does not always terminate with regularity as to time, as in the acute infectious diseases, but may become chronic, and the time and result uncertain.
In the slow, malarial diseases, according to this theory, the phagocytes finally acquire a domination more or less complete over the Bacilli malariæ; and this occurs not because the malaria has become less virulent, but because the phagocytes have acquired unwonted potency during the contest. This acquired domination of the phagocytes over one species of microbe seems not to be available against the inroads of other species. The exemption acquired in diphtheria and some other diseases seems partial as to degree and uncertain as to time.
One dreadful example of the failure of self-limitation of disease is found in hydrophobia. Here there is no natural stay or check to its fatality, and, although the most distinguished pathologists have given this question their best attention for many years, it seems questionable whether any life has ever been saved from hydrophobia. Large numbers of persons have been treated by inoculation for supposed hydrophobia, many of whom died, and the symptoms proved the hydrophobic cause; while in those who recovered no positive demonstration of true hydrophobia could be made, and the question of curability or prevention by inoculation remains undetermined.
M. Pasteur, the wizard micrologist, claims success in his battles with the rabies germs, and his brilliant achievements in other fields lend encouragement to expectant humanity. Jenner's vaccine discovery, by which millions of lives have been saved, encourages the sanguine belief that the principle of inoculation will, ere long, be made available for the preservation of countless human lives.
The method of M. Pasteur has been to obtain some of the positively fatal virus from the brain of a person or animal which had died from hydrophobia, and to reduce the germs through numerous generations by a system of modifying treatment until they have lost, in some degree, their fatal virulence, while at the same time they may have retained a protective activity within the limits of safety.
In the warfare with the pathogenic microbes the idea of employing certain species as our allies, and opposing them against the very dangerous ones, is brilliant, and there are many facts encouraging the belief that the kingdom of the microbes may be further divided against itself, through the natural voracity of its numerous clans. Surely any tactics and every means, agressive and defensive, must be made available against an enemy so insidious and so formidable.