It was only natural that the framers of our revenue acts, always on the lookout for new sources of revenue, should have turned their attention to the proceeds of insurance policies when they were dealing with the subject of death duties. It was natural for two reasons: first, the purchase of an insurance policy is nearly always prompted by some vague contemplation of death, and the receipt of the proceeds from a policy is intimately connected with death, in view of the fact that death normally is the event that brings about the maturity of the policy; and second, if the proceeds of insurance are not taxed, great opportunities for tax avoidance are opened to testators who desire to pass their property to special beneficiaries. The theory of taxation of the proceeds of insurance policies by death duty is that insurance is simply a method of building an estate by the investment of periodic savings.