The development of the modern industrial era in Europe, America, and the other parts of the world which have been colonized by Europeans, has seen gradual and progressive changes in the character of the human diet, which represent an experiment which was blindly entered into, and which is now proving a grievous failure, as attested by the pronounced tendency to physical deterioration. More and more, cereals, meats of the muscle type, and tubers have become the prominent articles which nourish the Western nations. With the great increase in population the production of dairy products has become more and more a precarious business, because of the keen competition of vegetable foods in the market. On the vast ranges of America, Australia, Argentina and elsewhere, in which there is but scanty rainfall, beef production has been economically successful and has tended greatly to discourage live stock production in regions better suited to the growing of farm crops. The dairy industry would scarcely have continued to exist until now had it not been for the discovery that the great bulk of the agricultural land of America is limited in its fertility by its low content of potassium, phosphorus, and in some places of lime, and soon becomes exhausted when cereal or other crops are grown continuously and are sold off the farms. Worn out farms exist in large numbers to-day in New England and New York and elsewhere in the East, and signs of soil depletion are evident in parts of the great wheat-growing belt in the northwest. We have no adequate sources of potassium and phosphorus with which to replace these indispensable plant nutrients. This was recognized years ago by scientific agriculturists, and the agricultural colleges and the U. S. Department of Agriculture have urged upon farmers the necessity of maintaining a flourishing animal industry as the only means of maintaining a permanent system of agriculture. By this means the crops are fed on the farm and the fertility is in great measure preserved.