First published in 1999. This is Volume XVII of nineteen in the Abnormal and Clinical Psychology series. Written in 1926 through this study is the general conclusion at which the author has been enabled to arrive by a study of the manic-depressive psychosis. Demonstrating that within we find every kind of feeling represented --even the most complicated--and on a more elaborate scale, so that each particular feature appears with greater clearness. Secondly there is a description and analysis of mixed forms at various levels, of those mental states in which different feeling-elements are in operation simultaneously and with opposite and contrasted effects, so that the elements are set off one against another.