He pours some liquid onto the teaspoon and offers it to the chemist, and says “Could you taste this for me, please?”
The chemist takes the teaspoon, puts it in his mouth, swills the liquid around and swallows it.
“Does that taste sweet to you?” says Paddy.
“No, not at all,” says the chemist.
“Oh that’s a relief,” says Paddy.
“The doctor told me to come here and get my urine tested for sugar.”
(Sorry I offend anyone, but thought this was too funny not to share)