EMBRYOLOGY AND HUMAN MORTALITY 143 



important are the fundamental embryological factors 

 in determining the mortality of man. Of the three local- 

 ities compared, England and the United States may be 

 fairly regarded as much more advanced in matters of 

 public health and sanitation than Sao Paulo. This fact 

 is reflected with perfect precision and justice in the re- 

 lative proportion of the death rates from endoderm and 

 ectoderm. In the United States and England about 55 

 per cent, of the classifiable deaths are chargeable to endo- 

 derm and about 9 to 14.5 per cent, to ectoderm. In Sao 

 Paulo 62.6 per cent, fall with the endoderm, and but 6.3 

 to 8.4 per cent, with the ectoderm. Since public health 

 measures can and do affect practically only the death 

 rate chargeable to endoderm, this result, which is actually 

 obtained, is precisely that which would be expected. 



A question which naturally occurs is as to what the 

 age distribution of breakdown of ectodermic, mesoder- 

 mic, or endodermic organs may be. Are the endodermic 

 organs, for example, relatively more liable to breakdown 

 in early life, and less so later, as general observation 

 would lead one to conclude? 



To answer this and similar questions which come to 

 mind it is necessary to distribute the specific rates of 

 Table 9 upon an embryological basis. 



In Figure 39 the result of doing this is shown for 

 males. We note that prior to age 60 the curve for the 

 breakdown of organs of endodermic origin lies at the 

 top of the diagram; next below it comes the curve for 

 thq breakdown of organs of mesodermic -origin; and 

 finally at the bottom the curve for the breakdown of or- 

 gans of ectodermic origin. All three of the curves have 

 in general the form of a specific death rate curve. The 

 rates for all three germ layers are relatively high in in- 



