ILLUSTRATIONS 15 



FIG, PAGE 



42. Influence of father's age at death upon longevity of offspring (After 



Bell) 156 



43. Influence of mother's age at death upon longevity of offspring (After 



Bell) 157 



44. Influence of age at death of parents upon the percentage of offspring 



dying under 5 years (After Ploetz) 178 



45. Snow's results on selective death rate in man 182 



46. Male and female fruit fly {Drosophila melanogaster) (From Morgan) . 187 



47. Life lines for Drosophila melanogaster 188 



48. Life lines for different inbred lines of descent in Drosophila 192 



49. Life lines showing the result of Mendelian experiments on the dura- 



tion of life in Drosophila 195 



50. Distribution of poverty in Paris (.1911-13). (After Hersch) 202 



51. Death rates in Paris (1911-13) from all causes. (After Hersch) 203 



52. Trend of death rates for four causes of death against which public 



health activities have been particularly directed 230 



53. Trend of death rates from four causes of death upon which no direct 



attempt at control has been made 232 



54. Trend of combined death rate from the four causes shown in figure 



52 as compared with the four causes shown in figure 53 233 



55. Course of the weighted average death rate for the countries in the A 



and B groups, from typhoid fever 236 



56. Like figure 55, but for diphtheria and croup 237 



57. Record of malaria control by antimosquito measures, Crossett, Ark., 



1916-1918. (From Rose) 241 



58. Disappearance of yellow fever from Guayaquil, Ecuador, as a result of 



control measures. (By permission of International Health Board) 242 



59. Showing the change in percentage which deaths were of births in 



each of the years 1912 to 1919 246 



60. Theoretical curve of population growth 249 



61. Curve of growth of the population of the United States 250 



62. Curve of growth of the population of France 251 



63. Curve of growth of the population of Serbia 253 



64. Growth of a Drosophila population kept under controlled experi- 



mental conditions 254 



