The line of demarcation made between infancy and childhood, both by ancient and modern writers, has always been arbitrary. I would draw the line between the two, at a period of time which appears to me to be the most natural, the most simple, and least likely to lead the reader into the danger of misapplying any part of the practical directions of this, or any future chapter of the work. We will consider, then, that Infancy, commencing with birth, extends to about the end of the second year, when the first dentition is completed.