A paper was read several years ago before the members of a society in London, in which the author maintained that mental labor was never injurious to a perfectly healthy human organization, and that the numerous cases of break-down, which are commonly attributed to excessive brain-work, are due, in reality, to the previous operation of disease. This is one of those assertions which cannot be answered in a sentence. Concentrated within the briefest expression it comes to this, that mental labor cannot produce disease, but may aggravate the consequences of disease which already exists. The difficulty of testing this is obvious; for so long as health remains quite perfect, it remains perfect, of course, whether the brain is used or not; and when failure of health becomes manifest, it is not always easy to decide in what degree mental labor may have been the cause of it. Again, the accuracy of so general a statement cannot be proved by any number of instances in its favor, since it is universally admitted that brain-work is not the only cause of disease, and no one affirms that it is more than one amongst many causes which may impede the bodily functions. When the poet Wordsworth was engaged in composing the "White Doe of Rylstone," he received a wound in his foot, and he observed that the continuation of the literary labor increased the irritation of the wound; whereas by suspending his work he could diminish it, and absolute mental rest produced a perfect cure. In connection with this incident he remarked that poetic excitement, accompanied by protracted labor in composition, always brought on more or less of bodily derangement. He preserved himself from permanently injurious consequences by his excellent habits of life. A very eminent living author, whose name I do not feel at liberty to mention, is always prostrated by severe illness at the conclusion of each of his works; another is unwell every Sunday, because he does not write on that day, and the recoil after the mental stretch of the week is too much for him.