It was a fact of life for Escher that his health deteriorated during the late 1960s. He struggled with it his entire life, but this particular decade was a succession of good and bad spells. During the good spells, he was alert and active; during the bad ones, poor health dominated his life. In the spring of 1969 he had a good spell again and he filled his time with a number of lectures, produced 40 prints of
Day and Night (although he thought that this was a waste of his precious time) and devised and created a new print.
It was working on something new that made him especially happy. In a letter to his son George, he wrote that he was 'wild with excitement' about
Snakes. In the winter of 1967/1968, he had extended his
Metamorphosis II to
Metamorphosis III, but the last new print preceding it originated from autumn 1966. He therefore devoted himself wholeheartedly to this new stream of creativity, despite being afflicted by poor health. The development process took a great deal of energy, and he often had to stop work in order to take a break.