Prof. Emil Fisher, of Berlin, has shown that nitrogen, or rather protein, is our principal nourishment, and he has made considerable progress in analyzing it. He has even made some of its simpler forms - but it is merely academic knowledge. We must get our nitrogen food from plant activities, and they must receive it in solution through the roots. To replace the nitrogen extracted by the rootlets, farmers had a supply in their manures, but it proved insufficient. We discovered and used up the fossil manures of the guano beds, and then we began the use of ammonium sulphate derived from coal tar, but this, too, is limited in amount, and finally we find that the Chili saltpeter beds, our next supply of nitrogen, will be exhausted in some centuries at the present rate of exportation. Some free nitrogen is fixed in the soil by electric discharges, but so small in amount as to be of no practical importance. Prof. E. Henry, of Nancy, France, has discovered another source of nitrogen in the soil of forests. He has proved that the leaves in decaying, actually accumulate nitrogen, so that after they rot it is richer than before, and it is supposed to be a result of bacterial growth. The increase in forest-soil nitrogen is greater than the losses taken out by the tree roots - hence, forest soils increase in nitrogen, and we have another way of storing it.

Recent botanical literature puts an entirely new face upon the nitrogen question, and the discoveries show that our danger of nitrogen starvation is quite remote. Prof. Henry A. Weber* in his address as Vice President of the American Association for the Advance of Science,*  gave a resume of these discoveries relative to the absorption and storing up of free nitrogen of the air by certain classes of plants. It was formerly taught that plants could utilize only the nitrogen of the soil, and if the soil had no nitrogen the plant would have no more than that contained in the seed from which it grew, and would die of nitrogen starvation eventually. The early investigators proved that plants could not directly assimilate the free nitrogen of the air, and it is only in recent years that it has been shown that certain plants can utilize it indirectly through the intervention of bacteria. The legumes, and especially alfalfa and the clovers, are now known to harbor certain bacteria in their roots, and these cause the peculiar tubercles characteristic of these plants. It is a pure case of commensalism, the plant giving certain things to the bacteria, and the latter are able to absorb the free nitrogen of the air in the soil, and fix it into compounds, which are utilized by the plant. Thus peas and other legumes can grow in soil free of nitrogen, provided they are infected with the necessary bacteria. Whereas, in soil free of nitrogen, legumes not infected, and all other plants, infected or not, will cease to grow as soon as they use up the nitrogen in the seed, and will then die of nitrogen starvation.

After a clover crop, the roots have thus enriched the soil, and this explains the practical fact utilized by farmers for thousands of years, that if they want large yields of grain or other plants, which are able to use only the soil nitrogen compounds, they must precede the crops by one of clover, or peas, or other legumes. These recent observations "point out the way of securing from the free nitrogen of the air an ample amount of combined nitrogen to meet all the requirements of intensive farming. They make the farmer independent of the natural deposits of nitrogenous fertilizers, and furnish him the means of preventing his helplessness, in case these sources of plant food should become exhausted or otherwise available." In the above paper by Weber, the term nitrogen starvation is used to describe the condition of those plants deprived of sufficient nitrogen. It has never before been applied to animals, because they so promptly die in the struggle for existence. Hence, we have not noted it in man, the only animal which, through serious overpopulation, is deprived of the necessary amount of nitrogen.

* Ohio State University.

*  Science, January 2, 1903.

Prof. T. J. Burrill* denied that the bacteria in the root-tubercles of legumes do absorb free nitrogen, but that it is the work of other bacteria in the soil, as in the forest forms. It is immaterial which do it, so that it is done - this detail is only a minor quarrel.

It can be said that we have heretofore depended upon bacteria to capture free nitrogen of the air, feed it to plants who store it up for us in the grain or grass, whence it makes its way to the bodies of cattle from which we in turn derive it. It is finally thrown away in our sewers. This method of increasing the nitrogen is already a commercial success. The dried bacteria are sold to the farmer who places them in water along with sugar and other foods, so that they multiply enormously. This water is then sprinkled on the soil or the grains, inoculating them with the bacteria which are to feed nitrogen to the new plant.* 

Yet all this does not give us nearly as much nitrogen as we will need. The outlook seemed to be rather bad with prospects for a reduction of our saturation point, when science again stepped in, and by a series of discoveries has actually increased our nitrogen food by obtaining it from the air. There are 33,880 tons of the gas pressing upon each acre of ground, and this is the total amount of nitrogen in 1,500,000 tons of saltpeter, and it is found that we can capture all we want without resorting to bacteria. Sir Wm. Crookes, President of the British Association for the Advancement of Science, delivered at the 1898 meeting, in Bristol, a doleful address predicting nitrogen exhaustion in 1931, at our present rates of consumption. He failed to note the tremendous wheat areas still available, yet all this land needs nitrogen eventually or it will not bear wheat, and it is nevertheless, a question of nitrogen whether we have or have not millions of acres of new land easily exhausted. We cannot get something from nothing, to get nitrogen out of the soil we must put it in. Sir Wm. Crookes gives the solution himself in his own invention whereby we can get the nitrogen of the air in oxides by means of electricity. Companies have been formed for this very purpose, using the Niagara power here, and other water powers in Norway, to make nitric acid and other nitrates, and it is freely predicted that this invention will enable us to get unlimited fertilizers when we need them. The process has not yet proved commercially practicable for the production of fertilizers, but fortunately Dr. Adolph Frank, of Char-lottenburg, Germany, discovered a far better method of fixing the free nitrogen of the air by simply passing the gas over hot calcium carbide with which it combines to form calcium cyana-mide. This substance proves to be an excellent fertilizer, as good, or perhaps even better, than ammonium sulphate derived from coal tar. Dr. F. Lohnis, of Leipsic, has shown that it is readily attacked by soil bacteria, which reduce it to a soluble form readily absorbed by the rootlets. Companies are now formed in Europe to manufacture calcium cyanamide (Kalk-stickstoff) on a large scale. It might be of interest to note that the nitrogen gas is first obtained in a liquid form by liquefying the air and distilling off the oxygen. Doctor Frank's discovery was first mentioned by Prof. Ira Reinsert, in Science, January 1, 1904, and another process invented by Doctor Erlwein was described by J. W. Crowell, in Science, for January 29, 1904. The whole matter was soon put on a practical basis, and we have thus raised our saturation point again, because we can raise more food per acre than ever before. This means that there will shortly be many more millions of people in the world as a result of this one discovery.

* Science, September 30, 1904.

*  Mr. David Fairchild, of the Bureau of Plant Industry, has shown the great increase of nitrogen by inoculating soy beans. - Farmer's Bulletin, No. 315.