Here are some quick tips on how to distinguish classic crystal from plain glass. 1  Hold up a glass to the light. 2  If the glass acts as a prism and you see a rainbow you are holding crystal. 3  If not, it is just plain glass. 4  When struck, crystal produces a musical ring. 5  Glass does not.
Hormonal control of menstrual cycle. The ovarian hormones circulate in the blood and are excreted in modified forms in the urine. Estimation of the urinary output by chemical methods gives an indication of the blood levels and of the total production of these substances.
The role hormones play. The menstrual cycle is controlled by the hormones oestrogen and progesterone. Oestrogen is produced by the ovaries and makes the lining of the uterus repair itself and grow again after menstruation. Progesterone is produced by the empty follicle in the ovary after the egg has been released. This hormone maintains the lining of the uterus during the second half of the menstrual cycle.