Measures against infectious diseases as aiding in the prolongation of life—Prevention of syphilis—Attempts to prepare serums which could strengthen the higher elements of the organism Attacks of infectious diseases incurred during life frequently shorten its duration and it has been observed that most centenarians have enjoyed good health throughout their lives. Syphilis is the most important of these diseases. It is not really a cause of death itself, but it predisposes the organism to the attacks of other diseases, amongst the latter being some particularly fatal to old people, such as diseases of the heart and blood-vessels (angina pectoris and aneurism of the aorta) and some malignant tumours, especially cancer of the tongue and of the mouth. To lengthen human life, it is a fundamental necessity to avoid infection by syphilis. To reach this result everything must be done to spread medical knowledge about such diseases. It is absolutely necessary to overcome the deeply rooted prejudice in favour of concealing everything relating to sexual matters. Complete information should be widely spread as to the means of protecting humanity against this awful scourge. It has now been possible to apply experimental methods to the investigation of this disease, and science has obtained a series of results of the highest practical utility. Prof. Neisser of Breslau, one of the most distinguished of modern venereal physicians, has summed up the present state of knowledge of these matters in the following lines.[116] “It is our duty as medical men,” he says, “to recommend strongly as a means of disinfection in all possible cases of contagion the calomel ointment which Metchnikoff and Roux have advised.” It is to be hoped that future generations, by following this advice, will see an enormous diminution in the number of cases of syphilis. Syphilis, however, although a very important factor, is not alone in shortening the life of man. A very large number of persons die prematurely although they have not contracted that disease. We do not know the duration of human life before the arrival of syphilis in Europe, but there is no reason to think that it was very different from what it is to-day. We must, therefore, try to prevent as many infectious diseases as possible, and recent advances in medicine have made this task much less difficult. Pneumonia, it is true, the most common infectious disease amongst the old, cannot yet be easily avoided. All the anti-pneumonic serums which have hitherto been prepared have turned out to have little efficacy; but there is no reason to give up the hope that this problem will yet be solved. Diseases of the heart, which are common in extreme old age, are particularly difficult to avoid, because in most cases we do not know sufficiently well their primary causes. In so far as they depend upon intemperance or infectious diseases such as syphilis, they can be avoided by the employment of suitable measures.