A number of elements pass from the feed and/or water into the hen's blood, from there into the egg, and finally into all of the chick's tissues and chick's blood. These are aluminum, barium, calcium, copper, iron, magnesium, phosphorus, potassium, rubidium (?) silicon, sodium, strontium, titanium and vanadium. Manganese and zinc were each absent from one organ and the chick's blood. Of the ‘trace’ elements, aluminum, barium, copper, silicon, strontium, titanium and zinc were quite uniformly distributed among the tissues. There is a group of ‘trace’ elements more concentrated in the hen's blood and/or egg than in the feed and it appears reasonable that these are of high physiological importance. These are barium, iron, strontium and vanadium. The importance of iron is of course well known. The selection of barium and strontium may be caused by the inability of the hen's organism to distinguish these elements from calcium. The selection of vanadium is more difficult to explain: it is present in 4 plus quantities in the blood of both chick and hen, in the femur, heart, kidney and lung, suggesting some function associated with the hematopoietic organs. There is a group of three elements whose presence in the newly hatched chick is unnecessary or harmful. These are boron, fluorine and silver. Boron although present in the food and water was found only in the egg yolk. Fluorine was present in the water in a concentration of about 2 p.m.m. It was not present in a sufficiently large amount to be demonstrated in the eggs, bloods or soft tissues. It was present in one femur and therefore must have been present in the egg from which this femur was evolved. This element is most probably of no physiological importance in any amount and when present in drinking water to the amount of more than 1 p.m.m. has a toxic effect upon the developing enamel of children's teeth. Silver was present in the water. It was not demonstrated in the hen's blood, egg yolk, chick blood or tissues with the exception of one femur. Chromium, lead and molybdenum were present in approximately equal amounts in the hen's blood and in the feed and water, but were not constantly present in the eggs. Although the hen tolerates these elements in her own blood stream, she attempts to reject them for the formation of her eggs. The presence of these elements is tolerated in the adult organism but their presence is not necessary for the functioning of the chick and may be harmful. When the chicks contained these elements, molybdenum was found principally in the liver, lead in the lungs and chromium in the brain and eye. While we expect the accumulation of harmful heavy metals in the liver, the accumulation of chromium in the brain, and lead in the lung is surprising and at present unexplained. Manganese was present in greater quantity in the yolks as compared with the hen's blood and was absent from the egg white and egg shell. It was concentrated in the liver and appeared in slightly lesser amounts in the kidney and gizzard. Its absence from the chick's blood and its presence in all of the tissues with the exception of the eye indicates a probable inadequate supply of this element which is of general nutritive importance.