From the sheet music at Indiana University:


THE LAUGHING SONG
Trio: Lina, Fritz, and Muller.
Words by Vincent Bryan. Music by Harry Von Tilzer.
New York: Harry Von Tilzer Music Pub. Co., 1909.

1. MULLER: There are times you feel silly.
You laugh, willy-nilly,
  Without any reason at all.
At some tale or ditty
That's not bright or witty,
  In spasms of laughter you'll fall.
Ev'ry laugh is contagious.
Sometimes it's outrageous.
  You laugh till you can't get your breath.
Some thought wave mesmeric
Will make you hysteric.
  You laugh yourself nearly to death.

CHORUS. MULLER/LINA: Ha ha ha! Ha ha ha!
It's hysterical laughter you really can't stop!
Ha ha, La! Ha ha ha!
Pretty Lina is laughing at you, you old fop!

LAUGHING CHORUS:
Ha ha ha ha ha ha ha ha ha ha ha ha!
Ha ha ha ha ha ha ha ha ha ha ha ha!
Ha ha ha ha ha ha ha ha ha ha ha ha!
Ha ha ha ha ha ha ha ha ha ha ha ha!
Ha ha ha ha ha ha ha ha ha ha ha ha!
Ha ha ha ha ha ha ha ha ha ha ha ha!
Ha ha ha ha ha ha ha ha ha!
Ha ha ha ha ha ha ha ha ha!

2. LINA: When you know why I'm laughing,
You'll soon stop your chaffing.
  You're his daughter's husband, 'tis true.
You married for money,
But won't it be funny
  If that money don't come to you?
You have taken his daughter.
You'll have to support her.
  There's one thing you never foresaw:
Since you've wed Christina,
Her Pa'll marry Lina,
  And I'll be your mother-in-law!