It is Masuda's word that "If you spend a day with Sensei (indicates Saigo, literally means 'teacher'), you will feel one-day amount of humanity, if you spend three days with Sensei, you will feel a tree-day amount of humanity"; this word is quoted by Ryotaro SHIBA in his book.
司馬遼太郎も著書で引用した「1日先生に接すれば1日の愛があり、3日接すれば3日の愛がある」とは増田の言葉である。