are required in very small quantities, such as fluorine and iodine. Nothing is known of the exact need for the former, which must be required only in very small amounts, and the latter has been administered to a sick beast without effecting any improvement. Bush sickness occurs in coastal districts where sulphur is not likely to be wanting. Thus by a process of elimination one naturally arrives at iron as being the deficient element. Of the igneous rocks, the rhyolites, from which the bush-sick soils are derived, are among those rocks which contain least iron. The rhyolitic froth—pumice—which forms the soils, had no doubt been leached before being redistributed by a series of explosions in geological time, long after its formation in the volcano. This redistribution took place, according to Thomas,* A. P. W. Thomas, Report on the Eruption of Tarawera and Rotomahana, N.Z., Wellington, 1888, p. 19. not long before the Maori came to New Zealand, which would be probably about a thousand years ago. The amounts of iron extracted by hydrochloric acid from these pumice soils is of the order of 1 per cent., but the amount extracted in Dyer's 1-percent, citric-acid method for “available plant-food” gives about 0.03 to 0.07 per cent iron, whereas on non-bush-sick pumice soils the amount rises from 0.07 to 0.1 per cent., and on non-pumice soils it may rise to 0.3 per cent. These amounts for iron, compared with the standard amounts required for other constituents—phosphoric acid and potash—in the Dyer method, are high, but the standard for iron may need to be a high one. Another remarkable fact is that when bush-sick pasture is top-dressed with lime the animals become bush-sick sooner than on land which has had no treatment. This may be connected with the well-known fact that chlorosis of plants often occurs on sandy land containing an excess of lime. It is when one comes to the analyses of fodder plants that the first good evidence of iron deficiency is obtained. Pfeffer (Physiology of Plants, p. 428) states that ordinary plants are fully supplied with iron when 0.2 per cent, is present in the ash; but he is no doubt looking at the matter from the plant's point of view, and not from that of the animal which has to subsist on the plant. Analyses of the fodder plants, grasses, and clovers from the bush-sick country show that the iron content of the ash may sink to 0.05 per cent. Although the plant apparently continues to be healthy with this small amount of iron, it may not be sufficient for the animal. The analyses of clovers and grasses of the sick area show that the iron content is very much lower than that of similar plants growing on healthy country. Recent work by Dr. Orr, the Director of the Rowett Institute, Aberdeen, and his associates, has directed attention to the importance of inorganic foods in animal nutrition. An account is given of iron starvation occurring in pigs, when the mother was fed on a fish and vegetable diet containing 1,068 milligrams of food iron per day. It is suggested that the mineral-food requirement of each species of animal may be indicated by the composition of the milk of the species. The faster an animal grows, the more mineral food it requires. A young pig doubles its weight in ten days, but a calf takes forty-seven, a colt sixty, and a human child 180 days. Human milk and mares' milk contain one part, cows' two parts, and pigs' nine parts of iron in equal portions of milk. It is suggested by Kellner that an animal requires two to three times the amount of mineral food that it is able to store up. Sherman lays down the dictum that 12 milligrams of iron per day should be sufficient for an adult human being. Using this data and applying the corrections necessary—i.e., (a) for the increased