Iodine Fluorine traces. Silicon Manganese May be necessary; Aluminium found in minute Arsenic traces. It will be seen that there is a very respectable assemblage of elements within us and indeed within all animals, but not all are admitted to be necessary to life. Some of these elements may be there by accident, such as aluminium and silicon, but even those which are present in the rarest quantity may have a useful function to perform. Iron we know is indispensable, although only present to the extent of 0.004 per cent:, and iodine occurs in even smaller proportions but that also is necessary to life. An omission from this list is that of zinc and copper, both being present in traces, and since boron has been found to be necessary for the growth of some plants possibly this also should be added. In this address consideration will be confined to those mineral elements usually held to be necessary to animal life. Researches concerning mineral foods have been forced into prominence in the agricultural world owing to very puzzling troubles which affected some farming communities, both in old pastures in the old world, and in new pastures in recently settled areas in the New World of America, and in the newest settled world of South Africa, Australia and New Zealand. Animals ultimately failed to thrive when pastured on land where there was apparently plenty to eat, yet when they were removed to land where no such trouble exists the same animals not only recovered but often soon out-distanced in condition the animals native to that farm. These troubles are now generally referred to as “deficiency diseases.” The word “ultimately” is used advisedly, as imported stock do thrive, for periods extending over months, upon the same pasture on which, in time, they will become emaciated and eventually die of starvation. The reason that an imported animal may thrive for a time or may even fatten on “affected” country is that every animal possesses a store of each mineral element likely to be deficient, and while it is thriving it is using up that store, although it may take months to deplete it. In some forms of these mysterious troubles there were definite clinical symptoms, such as obvious deterioration in the bone texture, swellings in the bones and joints, and more or less lameness, and the cause of these was at once referred to extreme phosphorus deficiency in the diet. In other forms there was little to guide the veterinary pathologist as to the cause. Other characters of this class of trouble in stock were that the ailment did not spread but was restricted to definite areas, and in one deficiency disease blood from an affected animal could be transfused into the veins of a healthy animal without ill effect to it. The obvious conclusion, where wasting in numbers of stock occurs on pasture apparently sufficient in quality and quantity, and where pathologists cannot detect any ordinary disease or adequate parasitic trouble to account for the wasting, and where the pastures contain no mineral poison or poisonous weeds, is that there is some deficiency in the mineral foods,