Notwithstanding all of these advances, the generally recognized mental diseases, as late as 1895, included the following types:—mania, melancholia, dementia, imbecility, idiocy, general paresis, chronic delusional insanity or paranoia and senile insanity. This was in substance the psychiatry of Savage, Maudsley, Clouston, Blandfield, Régis, Chapin, Kellogg, Spitzka, Kirchoff, Berkley and many other well-known writers of a comparatively recent date. A new era in the history of mental medicine was ushered in by Kraepelin when the sixth edition of his "Psychiatrie" appeared in 1899. This established manic-depressive insanity and dementia praecox as clinical entities. Kraepelin called attention to the fact that excitements and depressions frequently recur in the same individual, often with frequent attacks but with no marked tendency towards mental enfeeblement. This class of cases he grouped together as manic-depressive psychoses and pointed out certain characteristics common to the excitements and depressions included. He showed that certain other forms of depression marked by anxiety, fear, restlessness, self-accusation, marked suicidal tendencies, etc., were common to the involutional period of life. To this anxious depression the name involution melancholia has been applied, although Kraepelin is now somewhat in doubt as to its differentiation from the manic-depressive group. To certain other cases characterized by emotional dulness, apathy, hallucinations with phantastic delusions, and in some types, mannerisms, negativism, stereotypy, verbigeration, etc., tending sooner or later towards deterioration, he attached the name dementia praecox. This included the hebephrenia of Hecker and the katatonia of Kahlbaum. Wernicke in 1906 advanced the hypothesis that psychical symptoms may be attributed to disturbances of various association mechanisms. These interruptions were to be found in various parts of the psychical reflex arcs. This included the psychosensory tracts or receptive mechanisms, the intrapsychical tracts or elaboration mechanisms and the psychomotor mechanisms. Manic-depressive psychoses were looked upon as representing a disorder of the intrapsychic mechanism, while dementia praecox was considered to be an illustration of a disturbance of the psychomotor mechanisms. This was an exceedingly interesting but purely theoretical scheme for putting psychiatry on a definite anatomical and pathological basis.