“ An old man who shrinks into himself falls into ways that become as positive and as much beyond the reach of outside influences as if they were governed by clock-work. ”
 Oliver Wendell Holmes Sr., The Autocrat of the Breakfast-Table (1858). copy citation

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“But to carry us out of maturity into old age, without our knowing where we are going, she drugs us with strong opiates, and so we stagger along with wide open eyes that see nothing until snow enough has fallen on our heads to rouse our comatose brains out of their stupid trances. There is one mark of age that strikes me more than any of the physical ones;—I mean the formation of Habits. An old man who shrinks into himself falls into ways that become as positive and as much beyond the reach of outside influences as if they were governed by clock-work. The animal functions, as the physiologists call them, in distinction from the organic, tend, in the process of deterioration to which age and neglect united gradually lead them, to assume the periodical or rhythmical type of movement.” source