Our knowledge of the precise cause of diphtheria, the Klebs-Löffler bacillus, has furnished us not only with the cure, but also with the means of preventing its spread. While under certain circumstances, particularly the presence of moisture and the absence of light, this germ may live and remain virulent for weeks outside of the body, careful study of its behavior under all sorts of conditions has revealed the consoling fact that its vitality outside of the human or some other living animal body is low; so that it is relatively seldom carried from one case to another by articles of clothing, books, or toys, and comparatively seldom even through a third party, except where the latter has come into very close contact with the disease, like a doctor, a nurse, or a mother, or—without disrespect to the preceding—a pet cat or dog.

More than this, the bacillus must chiefly be transmitted in the moist condition and does not float in the air at all, clinging only to such objects as may have become smeared with the mucus from the child's throat, as by being coughed or sneezed upon. As with most of our germ-enemies, sunlight is its deadliest foe, and it will not live more than two or three days exposed to sunshine. So the principal danger against which we must be on our guard is that of direct personal contact, as in kissing, in the use of spoons or cups in common, in the interchange of candy or pencils, or through having the hands or clothing sprayed by a cough or a sneeze.

The bacillus comparatively seldom even gets on the floor or walls of a room where reasonable precautions against coughing and spitting have been taken; but it is, of course, advisable thoroughly to disinfect and sterilize the room of a patient and all its contents with corrosive sublimate and formalin, as a number of cases are on record in which the disease has been carried through books and articles of clothing which had been kept in damp, dark places for several months. The chief method of spread is through unrecognized mild cases of the disease, especially of the nasal form. For this reason boards of health now always insist upon smears being made from the throats and noses of every other child in the family or house where a case of diphtheria is recognized. No small percentages of these are found to be suffering from a mild form of the disease, so slight as to cause them little inconvenience and no interference with their attending school. Unfortunately, a case caught from one of these mild forms may develop into the severest laryngeal type. If a child is running freely at the nose, keep it at home or keep your own child away from it. A profuse nasal discharge is generally infectious, in the case of influenza or other "colds," if not of diphtheria.

This also emphasizes the necessity for a thorough and expert medical inspection of school-children, to prevent these mild cases from spreading disease and death to their fellows. By an intelligent combination of the two methods, home examination of every infected family and strict school inspection, there is little difficulty in stamping out promptly a beginning infection before it has had time to reach the proportions of an epidemic.

One other step makes assurance doubly sure, and that is the prompt injection of all other children and young adults living in the family, where there is a case of diphtheria, with small doses of the antitoxin for preventive purposes. Its value in this respect has been only secondary to its use as a cure. There are now thousands of cases on record of children who had been exposed to diphtheria or were in hospitals where they were in danger of becoming exposed to it, with the delightful result that only a very small per cent of those so protected developed the disease, and of these not a single one died! This protective vaccination, however, cannot be used on a large scale, as in the case of smallpox, for the reason that the period of protection is a comparatively short one, probably not exceeding two or three weeks.

Suppose that, in spite of all our precautions, the disease has gained a foothold in the throat, what will be its course? This will depend, first of all, upon whether the invading germs have lodged in their commonest point of attack, the tonsils, palate, and upper throat, or have penetrated down the air-passages into the larynx or voice-organ. In the former, which is far the commoner case, their presence will cause an irritation of the surface cells which brings out the leucocyte cavalry of the body to the defense, together with squads of the serum or watery fluid of the blood containing fibrin. These, together with the surface-cells, are rapidly coagulated and killed by the deadly toxin; and their remains form a coating upon the surface, which at first is scarcely perceptible, a thin, grayish film, but which in the course of twenty-four to forty-eight hours rapidly thickens to the well-known and dreaded false membrane. Before, however, it has thickened in more than occasional spots or patches, the toxin has begun to penetrate into the blood, and the little patient will complain of headache, feverishness, and backache, often—indeed, usually—before any very marked soreness in the throat is complained of. Roughly speaking, attacks of sore throat, which begin first of all with well-marked soreness and pain in the throat, followed later by headache, backache, and fever, are not very likely to be diphtheria. The bacilli multiply and increase in their deadly mat on the surface of the throat, larger and larger amounts of the poison are poured into the blood, the temperature goes up, the headache increases, the child often begins to vomit, and becomes seriously ill. The glands of the neck, in their efforts to arrest and neutralize the poison, become swollen and sore to the touch, the breath becomes foul from the breaking down of the membrane in the throat, the pulse becomes rapid and weak from the effect of the poison upon the heart, and the dreaded picture of the disease rapidly develops.

This process in from sixty to eighty per cent of cases will continue for from three to seven days, when a check will come and the condition will gradually improve. This is a sign that the defensive tissues of the body have succeeded in rallying their forces against the attack, and have poured out sufficient amounts of their natural antitoxin to neutralize the poisons poured in by the invaders. The membrane begins to break down and peel off the throat, the temperature goes down, the headache disappears, the swelling in the glands of the neck may either subside or go on to suppuration and rupture, but within another week the child is fairly on the way to recovery.

Should the invaders, however, have secured a foothold in the larynx, then the picture is sadly different. The child may have even less headache, temperature, and general sense of illness; but he begins to cough, and the cough has a ringing, brassy sound. Within forty-eight, or even twenty-four, hours he begins to have difficulty in respiration. This rapidly increases as the delicate tissues of the larynx swell under the attack of the poison, and the very membrane which is created in an attempt at defense becomes the body's own undoing by increasing the blocking of the air-passages. The difficulty of breathing becomes greater and greater, until the little victim tosses continually from side to side in one constant, agonizing struggle for breath. After a time, however, the accumulation of carbon dioxide in the blood produces its merciful narcotic effect, and the struggles cease. The breathing becomes shallower and shallower, the lips become first blue, then ashy pale, and the little torch of life goes out with a flicker. This was what we had to expect, in spite of our utmost effort, in from seventy to ninety per cent of these laryngeal cases, before the days of the blessed antitoxin. Now we actually reverse these percentages, prevent the vast majority of cases from developing serious laryngeal symptoms at all, and save from seventy to eighty per cent of those who do.

Our only resource in this form of the disease used to be by mechanical or surgical means, opening the windpipe below the level of the obstruction and inserting a curved silver tube—the so-called tracheotomy operation; or later, and less heroic, by pushing forcibly down into the larynx, and through and past the obstruction at the vocal cords, a small metal tube through which the child could manage to breathe. This was known as intubation. But these were both distressing and painful methods, and, what was far worse, pitifully broken reeds to depend upon. In spite of the utmost skill of our surgeons, from fifty to eighty per cent of cases that were tracheotomized, and from forty to sixty per cent of those that were intubated, died. In many cases they were enabled to breathe, their attacks of suffocation were relieved—but still they died.

This leads us to the most important single fact about the course of the disease, and that is that the chief source of danger is not so much from direct suffocation as from general collapse, and particularly failure of the heart.