APPLETONS' 



POPULAR SCIENCE 



MONTHLY. 



JANUARY, 1898 



THE ETIOLOGY AND GEOGKAPHIO DISTRIBUTION 

 OF INFECTIOUS DISEASES.* 



By GEORGE M. STERNBERG, M. D., LL. D., 



BURGEON GENERAL, UNITED STATES ARMY. 



IN a recent address before a medical audience I defined the term 

 " infectious " as follows : 



" It is hardly necessary to say that by ' infectious diseases f we 

 mean those diseases which result from the introduction into the body 

 of some disease-producing agent. And I think we are justified in 

 saying that an essential condition of infection is that the disease- 

 producing agent shall be capable of reproduction in the body of the 

 infected individual in other words, that it is a living organism. It 

 matters not whether this living organism is large or small; whether 

 it belongs to the animal or vegetable kingdom; whether it is located 

 in the skin as in scabies, in the muscles as in trichinosis, in the lym- 

 phatics as in erysipelas, in the solid viscera as in amoebic abscess of 

 the liver, in the intestine as in cholera, or in the blood as in relapsing 

 fever, the introduction and multiplication of the living infectious 

 agent constitutes infection." 



The terms contagious and infectious are not synonymous. A 

 disease is contagious when it is transmitted from the sick to the well 

 by personal communication or contact, more or less intimate; and all 

 contagious diseases are infectious i. e., they are due to the introduc- 

 tion into the body of a susceptible individual of a living germ. But 

 all infectious diseases are not contagious. Thus smallpox, scarlet 

 fever, measles, diphtheria, influenza, etc., are infectious diseases 



* From an address read before the National Geographic Society of Washington. 

 vol. lii. 23 



