1. McKendrick, Text-book of Physiology, " Special Physiology," 356 (writes: " Division of the vagi at once causes periodic breathing to disappear [in animals when the medulla has been divided above the respiratory centres], and in its place there are irregular respiratory spasms. It is clear, therefore, that periodic breathing occurs when the upper nervous tracts are inactive and when in these circumstances the vagi convey impressions to the respiratory centre. Hence it is that the Cheyne-Stokes phenomenon appears when the higher nervous centres are totally or partially inactive, or, at all events, when the upper brain tracts are not conveying impressions downwards.").