ABSTRACT
Tetracyclines easily penetrate through the placenta and label calcified tissues of fetus. They are also delivered to young with the mother's milk. Good labelling of fetal tissues and suckling young was obtained when pregnant and lactating rats received 25–50 mg/kg of tetracycline or 7–15 mg/kg of oxytetracycline with their food, daily during all the period of pregnancy and lactation; no influence of tetracyclines on the body weight of females was noticed. Tetracycline marks can be revealed on ground sections or on the surface of a bone or a tooth. Decalcification destroys the marks. After an animal dies, the tissues that were labelled with tetracyclines can be stored dry or preserved in ethanol. Alizarin red was the first substance used for vital labelling of bone and teeth and it was widely applied before the possibilities of tetracyclines were discovered. Alizarin stains growing parts of bones and teeth red; stained parts are distinguishable both in visible and in ultra-violet light.
