Every infant should be vaccinated. The proper time is between the third and sixth month, though the operation may be postponed if there be any disease of the skin, and in very delicate subjects, if there be no risk of exposure to small-pox. The point selected for the introduction of the virus should be on a part of the body that can be readily protected and kept at rest; the leg in infants, before the ages of creeping and walking, the arm in later life. If the first insertion be unsuccessful, it must be repeated after a month's interval, and continued efforts made until the end is attained. A second vaccination should be done before puberty, though an exposure, or any risk of exposure, always indicates immediate re-vaccination.