Tuberculosis

This diminution of the "young adult" type of death-rate has, however, been less marked in certain counties of Ireland, Scotland and Wales, and indeed, in agricultural communities everywhere, than in the larger centres of population. Brownlee, in the report quoted, suggested that these differences might be due to the exist ence of para-tubercle bacilli of unequal virulence, but later researches by Tulloch have failed to discover any antigenic vari ants in a large series of "human" tubercle bacilli investigated by him. It may be assumed, therefore, that the recession of the age-period of maximum mortality from early adult to later life implies a more protracted clinical type of pulmonary tuberculosis now than formerly and in the larger centres of population as com pared with the more sparsely populated agricultural districts.

Fall in Tuberculosis Mortality.

As will be seen from the appended table (extracted from the registrar general's Statistical Review of England and Wales for the Year 1924, Table 6, page 35) there has been, from 1838 onwards, a steady fall in the tuber culosis death-rate affecting both the pulmonary and all other forms of the disease. This fall, which has been observable in other civilized countries, though often claimed as evidence of the value of modern methods of prevention, was just as marked before the recognition of the infective nature of tuberculosis as after the discoveries of Villemin and R. Koch had given a definite direction to sanitary effort. Clearly therefore, some factor of natural adaptation must have been present to supplement the efforts of preventive medicine.

Those who favour the theory of an "hereditary disposition" to tuberculous infection see in this diminution of mortality the result of the dying off of susceptible stock and the survival of the more resistant. Others consider that, with the wide dissemina tion of infection resulting from the agglomeration of large num bers of persons into urban communities, there has been at work a factor of natural auto-immunization, individuals acquiring various degrees of resistance as the result of mild and repeated infections.

In favour of the latter theory, it may be said that "acquired immunity" plays a part in limiting the spread of other bacterial diseases, that even the most susceptible animals may be made relatively resistant to tuberculosis through mild laboratory infec tions and that a high degree of resistance in any given community, as evidenced by a relatively low death-rate and a relatively chronic clinical type, goes hand in hand with a wide diffusion of infection as proved by tuberculin tests.

Prevention.

Man is liable to infection from two main sources, the first and infinitely the more important being infected persons and the second, milk from infected cows.

Not all infected persons are equally infective. Those suffering from the chronic type of pulmonary disease with cavities are, perhaps, the most dangerous of all, such cases producing, as a rule, copious expectoration of a sputum heavily charged with bacilli while, being relatively resistant, they often survive for years and are well enough to remain at home. There exist, too,

cases whose symptoms are more suggestive of chronic bronchitis or asthma than of tuberculosis and who consequently remain undiagnosed, no precautions being taken. Not only the sputum of such persons but the droplets emitted in coughing and talking are sources of danger to others, while the excreted bacilli may accumulate on the clothing and bedding used by them and in the apartments which they occupy.

Such persons establish the greatest concentration of infective matter within the home, and the smaller, the worse ventilated and the more crowded the home, the more massive the infection and the more serious the danger to others. In the home contact with susceptible persons is most likely—for the home is the nest for infants and young children. It is upon the homes and the families of infected persons that preventive measures must be focussed.

Adequate provision of hospital and sanatorium accommodation is also a prime necessity so that infected persons may be removed from amongst their still healthy relatives. The use of sputum flasks, the ventilation of rooms, provision of good food for de pendants—all these will help. In France, promising results are being attained on the Grancher System by which the young children of tuberculous parents are placed with selected foster parents in country districts.

Another interesting line of prophylactic effort now under trial in France is the protection of the infants born to tuberculous parents by "vaccination" with living but attenuated tubercle bacilli. A. Calmette and C. Guerin have succeeded, by special cultural methods, in so reducing the virulence of a selected bacillary strain that it no longer produces tuberculosis but merely a transitory and benign infective process accompanied, however, by the development, in experimental animals, of a high degree of resistance against re-infection by virulent strains. This vaccine of Calmette (B.C.G.) is now being administered not only to calves but to the infants of tuberculous parents shortly after birth. So favourable have been the results of experiments on laboratory animals that there are grounds for hope as to pre vention of human and bovine tuberculosis. Results published by Calmette and his co-workers have, however, been criticized on statistical grounds (notably by A. Wallgren in Acta Pediatrica 1927, vii., 12o) and it will take years to evaluate the success or failure of these experiments. In the interval, the want of any specific preventive measure throws us back upon general meas ures of hygiene, attempts to diminish the pool of infective per sons by improved methods of treatment and the supervision, control and, where possible, isolation of infected persons through the machinery of the tuberculosis schemes of local authorities and by precautions against the sale or the use of milk containing living tubercle bacilli.