We who live in this age of plenty can hardly realise that food could ever be a problem. But far-sighted scientists have already begun to look forward to the time when there will be so many people on the earth that the farms and fields will not supply food for every one. It is a well-known fact that the population of the world is increasing enormously. Think how America has been expanding; a whole continent overrun and settled almost within a century and a half! Nearly all the land that can be successfully farmed has already been taken up, and the land in some of the older settled localities, like Virginia and the New England States, has been so steadily cropped that it is failing in fertility, so that it will not raise as much as it would years ago. In Europe no crop at all can be raised without quantities of fertiliser. While there was yet new country to open up, while America and Australia were yet virgin soil, there was no immediate cause for alarm; but, as no less an authority than Sir William Crookes pointed out a few years ago in a lecture before the British Association, the new land has now for the most part been opened and tamed to the plough or utilised for grazing purposes. And already we are hearing of worn-out land in Dakota--the paradise of the wheat producer. The problem, therefore, is simple enough: the world is reaching the limits of its capacity for food production, while the population continues to increase enormously: how soon will starvation begin? Sir William Crookes has prophesied, I believe, that the acute stage of the problem will be reached within the next fifty years, a time when the call of the world for food cannot be supplied. If it were not for our coming inventors and scientists it would certainly be a gloomy outlook for the human race. But science has already foreseen this problem. When Sir William Crookes gave his address he based his arguments on modern agricultural methods; he did not look forward into the future, he did not show any faith in the scientists and inventors who are to come, who are now boys, perhaps. He did not even take cognisance of the work that had already been done. For inventors and scientists are already grappling with this problem of food. In a nutshell, the question of food production is a question of nitrogen.