Bacterial infection

“ Bacterial investigations inaugurated after an epidemic is recognized, as has frequently been done, seldom lead to results of value, both because the local normal bacterial conditions are generally unknown at the commencement of the investigation, and because the most important time, the time of infection, is already long past before the first samples are taken. ”

“ However, Infection does not necessarily lead to disease. If the host’s immune system acts appropriately, the person can be infected not having the symptoms. Additionally, bacteria are not the only microorganisms able to make human beings sick. ”

“ Many pathological observations have proved, that certain micro-organisms require a so-called mixed infection, that is, that certain bacteria alter the cell substance of the host in such a way, that some other kind of bacterium finds conditions favourable for its existence. ”

“ Indeed, even after invasion the infectivity of the special disease, whatever it happens to be, will be materially modified by the tissues. When we come to turn to the micro-organisms which are pathogenic parasites we shall further have to keep clear in our minds that their action is double and complex, and not single or simple. In the first place, we have an infection of the body due to the bacteria themselves. It may be a general and widespread infection, as in anthrax, where the bacilli pass, in the blood or lymph current, to each and every part of the body ”

“ In this way conditions formerly believed to be the causes of disease are now recognized as playing their part in predisposing to the action of the true causal agent, viz. the bacterium. In health the blood and internal tissues are bacterium-free; after death they offer a most suitable pabulum for various bacteria; but between these two extremes lie states of varying liability to infection. It is also probable that in a state of health organisms do gain entrance to the blood from time to time and are rapidly killed off. ”

“ It is protected not only by the stratified epithelium, but also in various animals, by coats of hair, wool, feathers, etc. The secretion pressure of the healthy sweat and oil glands acts as an effective bar even to motile bacteria. Nevertheless a very slight injury only is sufficient to give normal surface parasites and other pathogenics, accidentally or purposely brought in contact with it, an opportunity for more rapid growth and even entrance for general infection. ”

“ Other bacteria than the acid-fast group are stained blue by Gabbet's method. Those most commonly found are staphylococci, streptococci, and pneumococci. Their presence in company with the tubercle bacillus constitutes mixed infection, which is much more serious than single infection by the tubercle bacillus. It is to be remembered, however, that a few of these bacteria may reach the sputum from the upper air-passages. Clinically, mixed infection is evidenced by fever. ”

“ We may say, then, that the effect the bacillus has on the host depends largely on the host. Not only does it depend on what the host is, but the particular condition of the host at the time of infection is of importance. Children are subject to many diseases that adults seldom have. Hunger, thirst, fatigue, exposure and other factors may make a person susceptible to the actions of certain bacteria that would be harmless under other conditions. ”

“ As the lymph contains elements necessary to the body, such as water, oxygen, albumins, carbohydrates, etc., their loss brings about body-waste and exhaustion from lack of nourishment. Again, bacteria produce a vast number [Pg 10] of compounds, some harmless and others highly poisonous.
The symptoms of a microbic disease are largely due to the absorption of poisonous materials from the area of infection. These poisons may be formed in the tissues by the action upon them of the bacteria, or they may be liberated from the bodies of degenerating microbes. ”

“ The inability to readily separate the typhoid germ, for instance, from the colon bacillus, an organism frequently found in milk, presents technical difficulties not easily overcome. The most potent reason of failure to find disease bacteria is the fact that infection in any case must occur sometime previous to the appearance of the outbreak. ”

“ Here again the science of bacteriology lends a helping hand, for data concerning the efficiency of disinfectants can be ascertained only by bacteriological technique. It then becomes the duty of the scientist to direct his entire attention to those factors which in themselves are sufficient to allow a foothold for many an infectious disease. It is no less a fact among domestic birds than with human beings, that infection may take place by contaminated food, the particular parasite or organism being transmitted in such manner. ”

“ 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 ”

“ When bacteria capable of producing disease are introduced into the system, either through the mouth or into the lungs or into the blood through some skin abrasion, the bacteria, finding there a congenial habitat, thrive, grow, and multiply. In some cases, this bacterial growth results only in breaking down the cell tissues at the point or in the vicinity of the place where growth occurs; for instance, if a cut is made with a dirty knife, that is, one carrying bacteria on the blade, and is not immediately washed out with an antiseptic solution, bacteria will grow and pus will form in the cut. ”

“ Bacteria are those minute organisms which under various names are the active causes not only of diseases but of all putrefaction, fermentation and like changes in dead organic matter. Like all living 386things they may be killed, and on this is based the whole theory of disinfection. Some are more hardy than others, under conditions which are frequently supposed to be unfavorable to them. Merely to destroy an unpleasant odor or to admit fresh air into a room does not mean to disinfect, and it is necessary to understand this clearly in the effort to purify rooms in the event of infection. ”

“ In these latter days of popular knowledge of scientific progress, but without precise information of details, bacteria are associated in the public mind with disease, especially of the epidemic form. While this prejudice is useful in stimulating the people to adopt and enforce preventive measures against conditions that tend to promote bacterial life in their homes and in their own persons, yet it should be understood194 that comparatively few of the great number and variety of bacteria are pathogenic, or disease producing, in man. ”

“ When bacteria fall upon bad ground, that is, upon healthy tissue, they do not grow, they do not spring up and multiply. Tired tissues, as has been abundantly proved by animal experimentation, are prone to infection. They are good soil for the growth of bacteria. It is true generally; it is true locally. A part that has been injured, for instance, a part that has been bruised without any break in the skin, without the entrance of any infection from the outside, is damaged by something that hurts its resisting power as fatigue does. ”

“ It is of high vitality and resists more prolonged exposure to high temperatures than most non-sporing bacteria. It is capable of lying latent in the tissues for long periods, for example, in the marrow of long bones, and of again becoming active and causing a fresh outbreak of suppuration. This organism is widely distributed: it is found on the skin, in the mouth, and in other situations in the body, and as it is present in the dust of the air and on all objects upon which dust has settled, it is a continual source of infection unless means are taken to exclude it from wounds. ”

“ For the chief symptoms of onset see page 318.
Persons vary in susceptibility to attack by different infective diseases. The intensity of an attack depends on the condition of the patient, and on the number and the virulence of the particular microbes infecting the patient. In certain families attacks of particular diseases are more severe, and attacks are more liable to occur than in others.
It has been shown in certain diseases that the cells and the fluids of the body have a protective effect against infection. ”

“ These infectious diseases are caused by several different species of bacteria that gain entrance to the tissues by way of wounds. The bacteria that cause pyaemia are transferred by the blood stream to different organs and produce multiple abscesses. In septicaemia, the bacteria may occur in immense numbers in the blood and produce a general infection of the tissues, causing a parboiled appearance of the liver, heart, voluntary muscles and kidneys, and enlargement of the spleen. ”

“ There is evidence that a mixed infection—that is, the introduction of more than one species of organism, for example, the tubercle bacillus and a pyogenic staphylococcus—increases the severity of the resulting disease. If one of the varieties gain the ascendancy, the poisons produced by the others so devitalise the tissue cells, and diminish their power of resistance, that the virulence of the most active organisms is increased. ”

“ The ideal treatment, however, of bacterial disease is to put into the blood a substance, like an antiseptic, which will kill the bacteria or neutralize their toxines, but which will not injure the tissues with which it is brought in contact. ”

“ The mere fact that such germs have at times been found, however, is of little significance in the matter of possible aerial infection. They never occur in any considerable numbers, and considerable numbers of germs are usually necessary to produce a disease. It is known that many bacteria on being cast out into the air from an infected source lose their virulence in the process of drying and soon die. Evidence that disease germs pass through the air from room to room of a house or from a hospital to its immediate surroundings always breaks down when examined critically. ”

“ The channels of infection by which organisms gain the vantage-ground afforded by the depressed tissues are various, and next to the maintenance of resistant tissues they call for most attention from the physician and surgeon. It is in this field of preventive medicine—that is to say, preventing infective matter from ever entering the tissues at all—that science has triumphed in recent years. It is, in short, applied bacteriology, and therefore claims consideration in this place. ”

“ As has been said, infection consists in the injury of the body by living organisms which enter it. The body is in relation to the external world by its surfaces only, and organisms must enter it by some one of these surfaces. It is true that the bacteria in the intestine—either those normally present or unusual varieties—may, under certain circumstances, produce substances which are injurious when absorbed ”

“ The animals generally employed in the study of the pathogenic properties of the various micro-organisms are:
Preparation.—Before inoculation, the experimental animals should be carefully examined, to avoid the risk of employing such as are already diseased: since it must be remembered that in a state of nature, as well as in captivity, the animals employed for laboratory inoculations are subject to infection by various animal and vegetable parasites, and in some instances such infection presents no symptoms which are obvious to the casual examination ”

“ 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. ”

“ 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. ”

“ Infection through milk, butter, and cheese is less common, the gravity of the disease in animals leading to an early suppression of the mammary secretion. In all such cases the infection enters through sores in the mouth or from the bowels.
Those cases in which the bacillus enters the system with the inspired [p. 940] air are probably the least numerous. Yet the germ may reach the lungs in fine dust, and then find in the delicate respiratory mucous membrane the most accessible of all channels into the system. ”

“ The qualitative discrimination of the bacteria present in dust has resulted in the discovery of, amongst other disease germs, the consumption bacillus, the lock-jaw or tetanus bacillus, bacteria associated with diphtheria, typhoid fever, pulmonary affections, and various septic processes. ”