by hand 与 by the hand的区别

给你几个例子看看：

by the hand

I shook Jane by the hand.
我和简握了手。

He clasped her by the hand.
他握住她的手。

by hand

The letter was delivered by hand.
那封信是派专人送去的。

The letter was written by hand.
这封信是手写的。

by hand ＿ 手工制作/ 手写的 /(专人)递送 /抓住

by the hand ＿ 握手/拉手

前者为帮助后者意为换句话说UNDERSTAND？