means "to pass the summer in a dormant state." Zoologically, it's the opposite of hibernate; metaphorically, it's my last three months.
Grading papers, tired. Drink lots of water.
18 January. In the factory until half past six; as usual, worked, read, dictated, listened, wrote without result. The same meaningless satisfaction after it. Headache, slept badly. Incapable of sustained, concentrated work. Also have been in the open air too little. In spite of that began a new story; I was afraid I should spoil the old ones. Four or five stories now stand on their hindlegs in front of me like the horses in front of Schumann, the circus ringmaster, at the beginning of the performance.