In works on sociology and politics it is a commonplace to use language derived from medicine when the writers are referring to features of society which are regarded as abnormal. This chapter introduces the science of sociology the concepts and terminology of disease. It deals with the question whether there is any utility in the analogy, or possibly more than the analogy, of society with the living organism. The chapter explores certain general resemblances between the general methods of medicine and those by which one must approach the evils of society. There is an overwhelming mass of evidence to the effect that repression does not remove the evil, but that at the best the repressed experience remains in existence, always liable to flare up into activity later in life, while in the less favourable cases it leads directly to a whole series of morbid symptoms which greatly lower vitality and efficiency.