These checks to conception, though they are very largely used, can hardly be defended on physiological grounds. Every interference with a natural process must be attended, to some extent at least, with physical injury. There is not much evidence that the injury is great, but in so far as an interference is unnatural, it is unhealthy, and there is much evidence to show that many of the checks advocated and used, are not only harmful but are quite useless for the purpose for which they are sold. It will be conceded by most, no doubt, that with those capable of bearing healthy children, and those unable to rear healthy ones when born, prevention by restraint, ante-nuptial or post nuptial, is a social virtue, while prevention under all other circumstances is a social vice. Happiness has been defined as the surplus of pleasure over pain. What constitutes pleasure and what pain varies in the different stages of racial and individual development. In civilized man we have the pleasures of mind supplementing and in some cases replacing the pleasures of sense. We talk, therefore, of the higher pleasures--the pleasures of knowledge and learning, of wider sympathies and love, of the contemplation of extended prosperity and concord, of hope for international fraternity and peace, and for a life beyond the grave. Happiness to the highly civilized will consist, therefore, of the surplus of these pleasures over the pains of their negation. Self-preservation is the basal law of life, and to preserve one's-self in happiness, the completest preservation, for happiness promotes health, and health longevity. The first law of living nature then is to preserve life and the enjoyment of it, and the pleasures sought, to increase the sum of happiness will depend on the sentiments and emotions, _i.e._, on the faculties of mind that education and experience have developed, in the race, or in the individual.