If any egg laying flock does receive an antibiotic, it is usually under the supervision of a veterinarian and only for a short period of time to treat a specific disease outbreak or for prevention of a recurring disease on that farm. What does Grade A mean? Eggs are graded based on their quality and appearance. Grade AA eggs have thick, firm whites and high, round yolks. Their shells are clean and unbroken. Grade A eggs are like Grade AA, but their whites are reasonably firm. Grade A eggs are usually sold in stores. Grade B eggs have thin whites and wider yolks. The shells are unbroken, but might show slight stains. How are eggs packed? An egg is placed in the carton with the large end up.
Arsenic has been known since ancient times, though probably in compound form rather than in its pure state. It is used in combination with other materials in pigments, poison gases and insecticides (such as Paris Green, calcium arsenate and lead arsenate) and is well known from former use as a rat poison.
In the environment, arsenic is combined with oxygen, chlorine, and sulfur to form inorganic arsenic compounds. Arsenic in animals and plants combines with carbon and hydrogen to form organic arsenic compounds. Inorganic arsenic compounds are mainly used to preserve wood.