Institutio Oratoria

For the orator depends not merely on his knowledge, which increases with the years, but on his voice, lungs and powers of endurance. And if these be broken or impaired by age or health, he must beware that he does not fall short in something of his high reputation as a master of oratory, that fatigue does not interrupt his eloquence, that he is not brought to realise that some of his words are inaudible, or to mourn that he is not what once he was.