This system is known in England as the four-course shift. Knowledge gained by successive generations of observant farmers has given us the key to what Nature had hitherto kept to herself, and to-day we know why the plan adopted by our forefathers was right, and why the rotation of crops was, and is, a necessity. Men of science are devoting their lives to the systematic study of Nature's hidden secrets, and by means of Agricultural Colleges, as well as private individual research, these discoveries are being given to mankind, and long before the soils of Argentina show any serious loss of nitrogen from continuous cropping, science will probably have established means of applying in a practical manner those methods already known of propagating the nitrogen-collecting bacteria which thrive on alfalfa, clover, peas, soya beans, and other leguminous plants. Almost every country is now devoting time, money, and energy to agricultural research work. In 1908 the Agricultural College at Ontario prepared no less than 474 packages of Legume Bacteria, and in 309 cases beneficial results followed from the application thereof to the soil; in 165 cases no improvements in the crops were noticed, this may, however, have been due to the want of knowledge of how to manipulate the bacteria, or to lack of experience in noting effects scientifically, but in any case the experiment must be considered successful when the results obtained were satisfactory in no less than 65 per cent. of the trials. No greater factor exists than the microscope in opening up and hunting out the secrets concealed in the very soil we are standing on. If soils were composed of nothing but pure silica sand, nothing would ever grow; but in Nature we find that soils contain all sorts of mineral matter, and chief amongst these is lime. Alfalfa thrives on land which contains lime, and gives but poor results where this ingredient is deficient. The explanation is simple. There is a community of interest between the very low microscopic animal life, known as bacteria, and plant life generally. In every ounce of soil there are millions of these living germs which have their allotted work to do, and they thrive best in soils containing lime.