Various theories have been advanced to explain the occurrence of an epileptic seizure, but none of these is entirely satisfactory. It has been supposed that there is a slight chemical change in the gray matter of the cerebral cortex, rendering it very unstable. If, now, the gray matter holds in store a large amount of nerve energy, an epileptic fit may be caused by a sudden and violent discharge of this nerve energy, either with or without a stimulus. Another recent theory is that advanced by Krainski. He found that the output of urea is greatly diminished for a day or more before the occurrence of a fit. In this disturbed metabolism the system is supposed to form ammonium carbonate instead of urea. This compound gives off ammonia, and Krainski believes that the epileptic fits are caused by the ammonia, but this view is contradicted by other authorities.