[Hitotsu Yukimoto] Sleepy girl (Madoromi Ningyou)

I really like this scene! A dance teacher (wearing a sexy leotard no less) is approached by some of her male students. The students are wearing protective dust masks over their face, supposedly because of a flu or something. Anyway, the male students convince the dance instructor to put on a dust mask. The mask contains chloroform! Before she realizes it, the dance teacher passes out. The male students begin to bind and gag her while she is unconscious!