This is the age of anxiety to give social help. I hold strongly the view that ere many of you are advanced in years the fundamentally important social help which is constituted by adequate medical attendance will be provided, for all who wish to have it thus, at the expense of the state, i.e., coöperatively by means of common charges on every member of the community according to his means, exactly as elementary education is now provided. This will involve radical reconstruction of the relationship between hospital and private medical practice, and will, I trust, include also the introduction of preventive medicine into the practice of every physician. But this is in the future. How can medical practice under present conditions, and how can non-medical social agencies, be made subservient to the fullest extent to the welfare of the community? A few elementary illustrations will show the many unexploited or only partially exploited or misused opportunities for efficient social help. The greatest science is to know the causes of things; and there is no branch of work in which this is more important than in medicine. But causation is complex. A given result commonly follows from a chain, or it may be a bundle of events: and as we shall shortly see the end links of the chain are oftimes joined, thus forming a circle. If a man shoots a companion with whom he has quarrelled, it may be urged that a more rigid system of license for the use of firearms would have prevented the calamity; that the companion was also quarrelsome; that the homicide had been the spoiled child of his mother and had not had a satisfactory up-bringing; and that he inherited from his father a violent temper; but none of these circumstances,—all of which may have contributed to the murder,—is likely to succeed in preventing the murderer from being hanged after due trial. It would be difficult to find a more striking instance of the linking of elements in causation than in the origin of a case of malaria. For the transmission of this disease two human beings, one already infected with the specific contagium, and a mosquito are required, and the chain of causation can be broken at the infecting person, by strict screening from mosquitos, and by the use of quinine; at the mosquito by preventing its emergence from the larval stage, and later by preventing its access to the patient; or at the prospective patient, possibly by prophylactic medication, more certainly by strict screening from mosquitos. Hence one might claim lack of segregation of infected persons, lack of screening of the healthy, failure to drain marshes, to apply oil to the surface of stagnant pools, or to adopt allied measures destroying the larvae of mosquitos as each of them the cause of malarial disease.