On the other hand are those who direct their efforts towards cultivating the soil. Reliable studies inform us that ninety per cent. of the human race is tuberculosis infected, and that infection occurs at a very early age, so that at twelve years few children have escaped it. Relatively a small number of those infected subsequently become tuberculous, so that something more than infection is necessary for tuberculosis to develop. What this something is we do not know. Time, manner, frequency, and intensity of infection play an important part. Apparently too there is a wide personal variation in susceptibility. To just what this personal factor is due we are not in a position to say, but certain general facts known about the distribution of tuberculosis afford us a clue to its interpretation. Tuberculosis, like most infectious diseases, thrives under the conditions that poverty induces. Inadequate housing facilities, insufficient food, filth, and sordid care are a few of these. If, as all must admit, the tubercle bacillus is more or less ubiquitous and few escape contact with it, then an important part of our campaign of prevention will be the raising of personal resistance so that when infection occurs it may be successfully overcome. Here is the field for wide social activity. Everything that makes for higher standards of living and for improved personal hygiene is a valuable arm against tuberculosis. Housing laws, child-labour laws, the wage question, municipal recreation centres, the liquor question, social service in all its departments, vacation lodges, open-air schools, factory inspection, and so on and so on, are all indirectly valuable anti-tuberculosis agitation. It is not my purpose to discuss the relative merits of the various phases of the anti-tuberculosis campaign. The death-rate from tuberculosis is falling steadily and rapidly, and it has fallen most rapidly in just those centres where the campaign has been vigorously pushed on a broad basis. Which phase of the work is responsible for the decrease or deserves the greatest credit, it is impossible to conclude from a study of available evidence. The same statistics are interpreted by one, for instance Cornet, as evidence of the efficiency of sputum prophylaxis; by another, for instance Hoffman, as evidence of the influence of improved economic conditions; by yet another, for instance Newsholme, as evidence of the value of hospitals for advanced cases; and finally by many, for instance Fränkel, as evidence of the undisputed value of all three factors. Which factor one emphasizes will depend largely upon one’s training and the field of activity in which one is engaged.