256 BIOLOGY OF DEATH 



fairly densely populated. It would have about 66 per- 

 sons per square mile of land area. 



It will at once be pointed out that many European 

 countries have a much greater density of population than 

 66 persons to the square mile, as, for example, Belgium 

 with 673, the Netherlands with 499, etc. But it must not 

 be forgotten that these countries are far from self- 

 supporting in respect of physical means of subsistence. 

 They are, or were before the war, economically self- 

 supporting, which is a very different thing, because, by 

 their industrial development at home and in their colo- 

 nies, they produce money enough to buy physical means 

 of subsistence from less densely populated portions of 

 the world. We can, of course, do the same thing, pro- 

 vided that by the time our population gets so dense as to 

 make it necessary, there still remain portions of the globe 

 where food, clothing material and fuel are produced in 

 excess of the needs of their home populations. 



Now 197,000,000 people will require, on the basis of 

 our present food habits, about 260,000,000 million calories 

 per annum. The United States, during the seven years 

 1911-1918, produced as an annual average, in the form of 

 human food, both primary and secondary (i.e., broadly 

 vegetable and animal), only 137,163,606 million calories 

 per year. So that, unless our food habits radically change, 

 and a man is able to do with less than 3,000 to 3,500 calories 

 per day, or unless our agricultural production radically 

 increases, which it appears not likely to do for a variety 

 of reasons which cannot be here gone into, it will be 

 necessary, when even our modest figure for the asymptotic 

 population is reached, to import nearly or quite one-half 

 of the calories necessary for that population. It seems 

 improbable that the population will go on increasing at 



