Glass breakage experiments were made which indicate two different mechanisms of fracture. The breaking process is dependent on the widths as well as the depth of the origin flaws. When the fracture is of the large, open type, the reciprocal of the breaking stress is a linear function of the depth of flaw; when the flaw is minute, the reciprocal of the breaking stress is a linear function of the square root of fracture depth.A pronounced strength increase was observed in cuts formed under various liquids and aged for various lengths of time. This increase took place about one hour after cutting and was interpreted as a rehealing phenomenon. Cuts made in air did not show the rapid strength increase.Cycle fatigue tests were also made on laths of glass and it was observed that there was an initial decrease in strength followed by an increase. This was interpreted as rehealing effect in the minute type of flaw.