"When water is heated to boiling... and one goes on heating it, the first thing that follows—without change of temperature—is a tumultuous expansion of freed and vaporised molecules. Or, taking a series of sections from the base towards the summit of a cone, their area decreases constantly; then suddenly, with another infinitesimal displacement, the surface vanishes leaving us with a point. Thus... we are able to imagine the mechanism involved in the critical threshold of reflection. ...[N]ervous systems followed pari passu the process of increased complication and concentration. Finally, with the primates, an instrument was fashioned so remarkably supple and rich that the step immediately following could not take place without the whole animal psychism being... recast and consolidated on itself. ...When the anthropoid... had been brought 'mentally' to boiling point.... Or... had almost reached the summit of the cone, a final effort took place along the axis. ...What was previously only a centred surface became a centre. By a tiny 'tangential' increase, the 'radial' was turned back on itself and... took an infinite leap forward. Outwardly, almost nothing in the organs had changed. But in depth, a great revolution... consciousness was now leaping and boiling in a space of super-sensory relationships and representations; and simultaneously... was capable of perceiving itself... for the first time."