No class of property is subject to more rapid changes in value than real estate. After an extensive advance the holder of a mortgage may be insufficiently protected by the equity in the property, even if his mortgage represents only 60 per cent of the current appraised value of the real estate pledged. It may be that the 60 per cent which he has loaned represents the total value or more than the total value a few years before. When a rapid advance in values occurs, tho it may be largely justified by the growth and development of the territory, there is sure to be present an element of speculation which is likely to carry prices beyond the point of reason. When the turn comes and a severe collapse takes place, its effects are extremely disastrous, because, unlike speculation in stocks or commodities, no short selling exists in real estate to temper the fall, and the immobile form of capital makes liquidation impossible. These considerations serve to show the need for great prudence in the purchase of real-estate mortgages. If the investor exercises due care in these particulars, he is reasonably sure of obtaining a very high-grade security; if he neglects these precautions, he may suffer severe loss of principal. No general figures are available which would indicate the degree of certainty attaching to the payment of interest upon real-estate mortgages. Certain classes of mortgages, such as those secured by unimproved real estate or dwellings, afford no direct security of interest payment other than the threat of foreclosure. Other classes, such as mortgages upon stores, hotels, or office-buildings, are often protected by a large income from the direct operation of the mortgaged premises, thus furnishing a security for the annual interest payment. The margin of protection in these cases varies greatly, so that no general conclusion can be drawn. The other characteristics of real-estate mortgages may be passed over more briefly. It is generally conceded that mortgages return a higher rate of income than can be obtained upon any other form of investment which affords equal security. This constitutes their chief advantage. Their chief disadvantage, on the other hand, lies in their entire want of convertibility. There is no market for real-estate mortgages, and except in special instances they can not be readily sold. The fact that they are not subject to quotation prevents them also from holding out any prospect of appreciation in value. Their very deficiency in this respect, however, constitutes an important advantage from another point of view. Since they are not quoted they can not shrink in market price in obedience to changes in financial and business conditions. The buyer of a mortgage is assured that he can carry his mortgage at par through periods when it may be necessary to mark down all negotiable securities subject to changing market quotations. This is frequently a matter of great importance.