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In this book the author represents the results of studies in the hygiene of vision, previously published in book form (El Uso Natural de la Vision, New York, D. Appleton & Company, 1924) with amplifications that extend the application of the principles involved in the general hygiene of attention. The book is divided into three parts. Part I deals with the general nature of attention and follows closely the lines laid down by Ribot. By the use of the tachorthoscope and other methods it is demonstrated that voluntary or artificial attention, like spontaneous attention, is an oscillatory activity requiring alternate contractions and relaxations for its normal performance. Efforts to maintain steady fixation of attention defeat its purpose and result in diminished acuity of perception as the result of fatigue. Continued practice of such voluntary muscular contractions results in the occurrence of spasms that involve both striated and unstriated muscle and