North Dakota in 1924 was traced to barberry bushes near Jamestown. So the stem rust on oats in Wisconsin was traced to barberries. Disease reduced the 1922 crop of potatoes and sweet potatoes about one-fifth. Peach orchards have been destroyed by the "yellows." The pear blight has often been serious. This is a native disease which we have exported to New Zealand. Our early attempts to grow grapes were often ruined by black rot and downy mildew. Again, we must remind ourselves that nature is unmoral, for fungi often attack and destroy insects. Diseases of Animals Domestic animals suffer from many diseases. Chickens are attacked not only by diseases which may spread rapidly in large flocks but which may sometimes be a threat to other animals. Thus there is an avian tuberculosis which often attacks swine, rendering them unfit for human consumption. In 1926 some 6.2 per cent of the chickens inspected in thirty-six states were tuberculous. Pig tuberculosis seems to be increasing and the pig appears susceptible to any type of tuberculosis. From the rat the pig gets the trichina which it may pass on to man. Hog cholera is the most serious disease of swine. "During the last four decades hog cholera has caused in this country animal losses ranging between $13,000,000 and $200,000,000, killing annually an average of 66 out of every 1000 hogs." 21 It has destroyed 130 out of every thousand swine in a year, appearing in great epidemics in 1887, 1897, 1913 and 1926. The losses of animals in nonepidemic years have often reached 3 or 4 per cent. Tuberculosis is the greatest prevalent enemy of our cattle. Not until about 1895 was it realized that bovine tuberculosis was a problem serious to man as well as to cattle and only in the last decade has a well directed campaign arisen. The distribution of this disease shows geographical differences as it hits the dairy herds more than range stock. In 1926 some 2.8 per cent of our cattle were tubercular but in some sections not over 0.5 per cent were affected while in others 23.6 were diseased. Individual herds have often shown a much higher rate. About 63 per cent of our dairy cattle and 36 per cent of the beef cattle were under supervision in 1926. The sickness rate is showing a steady decline as supervision increases.22 Cattle are subject to the attacks of epidemic diseases like the "hoof and mouth" disease which swept over sixteen counties of California in 1924 and resulted in the destruction of 58,791 cattle, 21,195 hogs, 28,382 sheep and 1,391 goats a total of 109,766 domestic animals, not to mention 22,214 deer in the Stanislaus National Forest to which the infection spread. In some sections great trenches were dug by steam shovels and the cattle driven into them for destruction. The loss was estimated at over $7,000,000. Later in the year there was a small outbreak in Texas, seemingly of separate origin. The California outbreak is believed to have started in hogs fed on refuse from Mare Island Navy Yard which contained some imported carriers of the disease. 23 Horses suffer from glanders and influenza and are not immune to tuberculosis. Dogs and cats suffer from rabies, which is very dangerous to man. Sheep are attacked by anthrax. Now that the nature of disease is fairly well understood the state and national government are coöperating to prevent the importation of disease carriers and to stamp out any infection that may appear. Gradually the producer is learning that safety depends on eternal vigilance. Probably in no other field has control of nature been of greater help to man. Even so we stand at the beginning rather than at the end of our development. REFERENCES 1. W. LIBBY, History of Medicine, pp. 3-6. 2. Ibid., p. 80. 3. W. RILEY, From Myth to Reason, p. 74. 4. P. DE KRUIF, Microbe Hunters. 5. W. W. KEEN, Review of Reviews, Feb., 1927. 6. J. F. SCHAMBERG, Vaccination in Relation to Animal Ex perimentation (1911). 7. A. M. SCHAEFER, quoted by, in Nation's Health (1926). 8. ROCKEFELLER FOUNDATION, A Review for 1926, p. 36. 9. H. COREY, National Geographical Magazine, May, 1917. 10. W. LIBBY, op. cit., p. 382. 11. W. C. GORGAS, Sanitation in Panama, pp. 73-74. 12. Ibid., p. 280. 13. W. OSLER, Evolution of Modern Medicine, p. 229. 14. HUNTINGTON and WILLIAMS, Business Geography, p. 100. 15. E. MAYO, The Outlook, Dec. 7, 1912. 16. New York Independent, Jan. 9, 1911. 17. J. SIMPSON, quoted by LIBBY, op. cit., p. 342. 18. W. LIBBY, op. cit., p. 342 19. W. W. KEEN, Animal Experimentation, p. 256. 20. Metropolitan Life Insurance Company, Statistical Bulletin No. 12 (Dec., 1923). 21. R. S. BIRCH, Hog Cholera, p. 231. 22. U. S. Live Stock Sanitary Association, Proceedings, 1926. 23. "Foot and Mouth Disease," Circular No. 400 (Dec., 1926), U. S. Department of Agriculture. CHAPTER IX POPULATION AND THE FOOD SUPPLY We look for rams and asses and stallions of good stock, and one believes that good will come from good; yet a good man minds not to wed the evil daughter of an evil sire if he but give her much wealth.-THEOGNIS, VI CENTURY B.C. THE WORLD POPULATION In all ages and climates mankind has observed the Biblical command, "Increase and multiply," more willingly and more uniformly than any other. We do not have detailed information for the entire world. Outside of a few countries all statements of population are estimates and many are crude guesses. All students agree in the belief that there has been an enormous increase during the Christian Era and that the net increase was greatest during the last century. A world population of some 850,000,000 in 1800 had doubled by 1900 to at least 1,750,000,000. To this there has been added yearly not less than 12,000,000, so the present total cannot be far from 2,000,000,000. If this rate were to continue there would be 5,000,000,000 human beings on earth by the year 2000, and 17,000,000,000 by 2100. Rossiter has estimated that the white races alone increased from about 30,000,000 in A.D. 1000 to 210,000,000 in 1800, but leaped to a total of 645,000,000 by 1915.1 If this rate were to be continued to 2020 the descendants of the European stock would number 1,980,000,000-approximately equal to the present population of earth. At the present rate the population of continental United States will double in fifty years, without any immigration, and Pearl estimates a total by 1980 of 175,000,000. The nineteenth century, then, was the era of the most rapid increase in numbers of men as well as that of the greatest advance in the technical arts. Whether or not these are related phenomena remains to be seen. In an earlier chapter we saw that the increase of any form of life caused certain problems; compelled some readjustments. How, then, did man provide for the needs of all these added millions? Population Movements One has but to compare the scattered population of Colonial days in America with the present population (1920) per square mile of Massachusetts (479), New Jersey (420), or Rhode Island (566), to realize that increased concentration has taken place. But we must not assume that this concentration is uniform. What has happened, in part, is a movement away from the farms to the industrial centers. In 1880 the rural population of the United States was 36,000,000; the urban, 14,000,000. In 1920 the rural population was 28,000,000; the urban 90,000,000. The actual farm population in 1910 was 12,659,000 but in 1920 it was only 10,953,000. There are agricultural counties which have not gained in population since 1870 and one-third of the counties of the country actually lost in population between 1910 and 1920. This shifting of population has not been limited to our country. During the last century there was a steady movement away from the older centers of culture to new and relatively unoccupied areas. In reality this was the greatest era of wandering known to man. The population of Canada increased from 251,000 to 5,370,000-some twenty fold. That of the United States increased 35 per cent per decade down to 1860. From 1820 to 1900 some 18,650,335 immigrants landed on our shores and not less than 16,000,000 |