Zinc oxide is the metal zinc that has been oxidized. The chemical formula is ZnO, 1 zinc atom and 1 oxygen atom held together by an ionic bond. Zinc oxide does occur in nature as the mineral zincite, but it is quite rare and commercially unavailable.
I have done a few stool samples in my time and have always just stored them in the fridge, until the next day to take them into the docs. Good luck hun I hope they get it sorted.
Milk, properly refrigerated, is still good about a week after its sell-by date. (As with many food products, a sniff test is usually sufficient to determine when milk is past its prime.) Cottage cheese, especially commercial Pasteurized varieties, lasts for 10-14 days after the date on the packaging.