THE AMERICAN NATURALIST [Vol. LIV 



From Table XI and the diagram a number of note- 

 worthy points can be made out. 



1. In the United States, during the decade covered, 

 more deaths resulted from the breakdown of the respira- 

 tory system than from the failure of any other organ 

 system of the body. The same thing 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 charge- 

 able to the alimentary tract is chiefly due, as Table VI 

 clearly shows, 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. 



2. In all three localities studied the respiratory system 

 and the alimentary tract together account for rather more 

 than half of all the deaths biologically classifiable. These 

 are the two organ systems which, while physically inter- 

 nal, come in contact directly at their surfaces with en- 

 vironmental entities (water, food, and air) with all their 

 bacterial contamination. The only other organ system 

 directly exposed to the environment is the skin. The 

 alimentary canal and the lungs are, of course, in effect 

 invaginated surfaces of the body. The mucous mem- 

 branes which line them are far less resistant to environ- 

 mental stresses, both physical and chemical, than is the 

 skin with its protecting layers of stratified epithelium. 



3. The organs concerned with the blood and its circu- 

 lation stand third in importance in the mortality list. 

 Biologically the blood, through its immunological mechan- 

 ism, constitutes the second line of defense which the body 

 has against noxious invaders. The first line is the resist- 

 ance of the outer cells of the skin and the lining epithe- 

 lium 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 system which, like the 

 industrial workers of a commonwealth, keep the body 



