STATISTICS: R. PEARL 
595 
is true of England and Wales. In Sao Paulo the alimentary tract takes 
first position, with the respiratory system a rather close second. The 
tremendous death rate in Sao Paulo chargeable to the alimentary tract 
is chiefly due to the relatively enormous number of deaths of infants 
under two from diarrhea and enteritis. Nothing approaching such a 
rate for this category as Sao Paulo shows is known in this country or 
England. 
In all three locaHties studied the respiratory system and the alimentary 
tract together account for rather more than half of all the deaths biolog- 
ically classifiable. These are the two organ systems which, while 
physically internal, come in contact directly at their surfaces with envi- 
ronmental entities (water, food, and air) with all their bacterial contam- 
ination. The only other organ system directly exposed to the environ- 
ment is the skin. The alimentary canal and the lungs are, of course, 
in effect invaginated surfaces of the body. The mucous membranes 
which line them are far less resistant to environmental stresses, both 
physical and chemical, than is the skin with its protecting layers of 
stratified epithelium. 
The organs concerned with the blood and its circulation stand third 
in importance in the mortality list. Biologically the blood, through its 
immunological mechanism constitutes the second line of defense which 
the body has against noxious invaders. The first line is the resistance 
of the outer cells of the skin and the lining epithelium of alimentary 
tract, lungs, and sexual and excretory organs. When invading organisms 
pass or break down these first two lines of defense the battle is then 
with the home guard, the cells of the organ systems which, like the indus- 
trial workers of a commonwealth, keep the body going as a whole function- 
ing mechanism. Naturally it would be expected that the casualties 
would be far heavier in the first two defense lines (respiratory and ali- 
mentary systems, and blood and circulation) than in the home guard. 
Death rates when biologically classified bear out this expectation. 
It is at first thought somewhat surprising that the breakdown of the 
nervous system is responsible for more deaths than that of the excretory 
system. When one bears in mind, however, the relative complexity of 
the two pieces of machinery, it is perceived that the relative position of 
the two in responsibility for mortality is what might be reasonably be 
expected. 
In the United States the kidneys and related excretory organs are 
responsible for more deaths than the sex organs. This relation is re- 
versed in England and Wales and in Sao Paulo. The difference is mainly 
