1813, Oct. 23. Signature to a document signed at Erfurt. After the defeat at Leipzig. 1814, April 4. Fontainebleau, prior to abdication. At St. Helena.] If passing emotions can have so great an influence upon handwriting, how much greater must be the effect when the centre or centres in the brain that control the writing mechanism are affected or destroyed by disease! Among the disturbances of handwriting due to defective control of the muscles we may include the so-called _tremor-writing_, which is common in old age, and the writing of people suffering from writers' cramp, an example of which is shown in the figure. [Illustration: Writers' Cramp] Other forms of defective writing may be the result of a paralytic stroke affecting the writing centre of the brain, which causes the patient either to form only parts of letters or endlessly to repeat the same letter under the impression that sentences are being formed, while in extreme cases there may be merely a succession of meaningless strokes in place of written characters. [Illustration: Specimen of Agraphia] The writing of insane people almost invariably shows the effect of mental disturbance. In some cases the form of the letters is changed, but they are still used in their right places. An illustration of this is given in the accompanying figure, which represents the signatures of the poet Lenau before and during his insanity. [Illustration: Writing of Lenau, the poet, before and during insanity] In other instances there is both alteration in the form of the writing and _paragraphia_, or the use of the wrong letters. Thus Hölderlin, the German poet, who became harmlessly insane in 1806 at the age of thirty-six, ever afterwards misspelled his name in the manner here shown. [Illustration: Signature of Hölderlin before and during insanity] A very interesting derangement of writing, which is probably due to the writing centre in one hemisphere of the brain becoming adapted to do the work of that in the other, is that commonly known as _mirror writing_. An example of this which came under the writer's observation is shown below. This shows the ordinary handwriting of a working woman of about sixty-six, who for the last three years has been paralysed in the right arm, and since then has produced mirror writing with her left hand. [Illustration: Mirror writing in paralysis]