In typhoid fever the methods followed in prevention are of a different character. The typhoid bacilli which cause typhoid fever are practically always taken into the body through the mouth, usually in drinking water or food. The commonest sources of infection are con taminated water, milk and oysters and also the direct infection of those in immediate contact with typhoid fever cases, by the transfer of the typhoid bacilli to the mouth on soiled hands or from eating or drinking utensils. Aerial infection plays a small part in the causation of this disease. The prevalence of typhoid fever has been very greatly restricted by the protection of the sources of water-supply, by the application of sanitary measures to the collection of milk, by proper disposal of sew age and in recent years by preventive inocula tion, which, in large armies, have made what was a formidable disease almost non-existent.
Sewage is the medium through which the typoid infection reaches the water-supply. Milk is infected, not when derived from the animal, but subsequently, from the washing of utensils with contaminated water or in some similar way. As yet no active measures have been adopted by the sanitary authorities to prevent the contamination of shellfish through the sewage-pollution of the water in which the shellfish beds are situated. This is probably a much more common source of infection than has been generally supposed. In the case of scarlet fever, measles, diphtheria, chickenpox, whooping-cough and mumps, prophylactic measures comprise the removal of the sick if possible to special isolation hospitals designed for this purpose and the adequate disinfection of clothing, rooms, furniture, bedding, etc., which may have become infected by contact with the sick. At present no other means are available, except in diphtheria, largely because of the lack of knowledge as to the exact causes of these diseases. In diphtheria, besides these measures, there is now a method for rendering the individual insusceptible to the disease for short periods by administering immunizing in jections of diphtheria antitoxin. By these in jections the individual may be rendered insus ceptible to the disease (as in smallpox by vac cination), but the immunity is of short dura tion.
Many sanitary authorities are now adopt ing measures for the prevention of tuberculosis, which causes more deaths throughout the civi lized world than any other single disease. Here again the problem of prophylaxis differs from that applicable to any of the other diseases mentioned. In tuberculosis the tubercle bacilli,
which are the cause of the diseases, are solely contained in the discharges from the diseased tissues, but the only form of tuberculosis (the disease may affect any organ or tissue of the body) in which the discharges containing the tubercle bacilli are likely to be a source of danger to others is tuberculosis of the lungs or pulmonary consumption. In this form, tubercle bacilli are frequently present in the expectora tion in almost incredible numbers. The pro phylaxis of tuberculosis is, therefore, prac tically comprised in the destruction of the ex pectoration of persons suffering from pul monary tuberculosis at the time of its exit from the body. If this could be absolutely, accom plished the transmission of tuberculosis from one person to another would be almost com pletely avoided. A common source of infec tion is probably present in the minute drops of atomized expectoration which are forcibly discharged into the air in coughing and sneez ing, unless the mouth and nose are covered during these acts. The prevention of tubercu losis only requires the exercise of scrupulous rare with regard to the expectoration, the re moval to isolation hospitals of those who are unwilling, too ignorant or unable because of weakness, to adopt proper precautions and the disinfection of rooms, with their contents, which have been occupied by tubercular patients. There remain to be considered, aside from this prophylaxis as applicable to the human being the measures necessary because of the possible transmission of the disease from animals, especially through the meat and milk of tubercular cows. But while this is a real danger, its importance has probably been greatly overestimated. It is now well known that tuberculosis very rarely exists at birth. It is never inherited, in the strict sense, and only in very exceptional instances does intra uterine infection occur.
General prophylaxis has as yet scarcely touched upon many of the other infectious and probably, to some extent at least, preventable diseases. The venereal diseases have been ig nored because the problem is so largely a social one. No preventive measures even promising in their character have been suggested for deal ing with them. The prevalence of the puerperal diseases has been very largely reduced through individual prophylaxis at the time of childbirth.