We are all born in one way but die in many. By international agreement a mortality code has been developed with fourteen general classes comprising 180 distinct units. Pearl would supplement this very unsatisfactory classification by the following: (1) circulatory system and blood-forming organs, (2) respiratory system, (3) primary and secondary sex organs, (4) kidney and related excretory organs, (5) skeletal and muscular system, (6) alimentary tract and associate organs concerned with metabolism, (7) nervous system and sense organs, (8) skin, (9) endocrinal system, (10) all other causes. This would show organological breakdown rather than pathological causation. The breakdown of the respiratory system is the chief cause of death, and next comes that of the alimentary tract; these together constitute half the deaths biologically classifiable. Next come troubles with the blood and circulation. We may conceive these as three successive defense lines, and it is against the first two of these that better health and hygiene have been chiefly directed, having been most successful with the respiratory system. Child-welfare, both pre- and post-natal, is by all odds the most hopeful direction of public-health activities. Pearl’s very important studies here confirm the conclusions others have reached, that early pubertal years show the lowest mortality rate, and he traces in detail for each age of life the mortality curves for each of the chief groups of disease. Very interesting are his conclusions touching the embryological basis of mortality in which he attempts to trace the causes of death back to the three primitive tissue elements, concluding that about 57 per cent of biologically classifiable deaths result from the breakdown or failure to function of organs arising from the endoderm, 8 to 13 per cent from those that spring from the ectoderm, while the remaining 30 to 35 per cent are of mesodermic origin. The ectoderm has been most widely differentiated from its primitive condition, as best illustrated by the central nervous system, the endoderm least differentiated, while the mesoderm is intermediate in this respect. Now, degrees of differentiation imply adaptation to the environment and the endoderm, which is least differentiated, is least able to meet vicissitudes. “Evolutionally speaking, it is a very old-fashioned and out-of-date ancestral relic which causes man an infinity of troubles. Practically all public-health activities have been directed toward overcoming the difficulties which arise because man carries about this antediluvian sort of endoderm.” Prior to the age of sixty the breakdown of organs of endodermic origin causes most deaths; next come breakdowns with organs of mesodermic origin, and lastly those of ectodermic origin. The rate for all these germ layers is relatively high in infancy, dropping to a low point in early youth. In infancy the chief mortality is due to endodermic defect; from about the age of 12 on, to faults