'On increasing the intensity of intermittent stimuli a rapid increase in frequency is necessary at first to produce fusion; after a certain frequency has been attained a further increase in intensity does not necessitate a further increase in frequency, this has been shown by Bellarminow [note: 'Archiv f. Ophthalmolgie, XXV. p. 25. 1889.'] and surmised by Haycraft [note: 'This Journal, XXI. p. 139. 1897.']: but on still further increasing the intensity of the stimuli fusion occurs with a decreased frequency.' (435)