After a corporation has been successfully started, the trust company may act as general fiscal agent, rendering all kinds of financial services to the corporation. The trust company is not usually given general powers, but only one or more special duties. One of these special functions is that of acting as transfer agent for a corporation. In this capacity the trust company keeps accurate records of all changes in ownership of the stock resulting from sales and purchases. It must be remembered that a stock certificate is merely an evidence of the ownership of a certain number of shares which can be transferred from one person to another only by entering this assignment in the stock book of the corporation. The certificate itself is non-negotiable, so the seller surrenders the old instrument and in its place the buyer receives a new one. Thus the chief duty of the transfer agent is to assure a "good delivery" or a clear title to the purchaser of the stock.