CAUSES OF DISEASE. 23 



fact that it is known to be the most frequent direct 

 cause of death. 



However, two infections may concurrently run 

 typical courses in the same individual. This happens 

 when scarlet fever and measles develop simultaneously. 



When an infectious agent attacks an 

 Secondary individual who is already suffering from 

 Infection. the attacks of another, we speak of the 



former as a secondary injection. Most 

 secondary infections follow as a result of the diminution 

 in vital resistance consequent upon the first infection. 

 Apart from the ordinary diseases of childhood, there 

 are two notable infections that are very commonly 

 secondary, because they take advantage of any depres- 

 sion in vital resistance that the body has suffered. 

 Their frequency and permiscuity are so well established, 

 that every precaution should always be taken to guard 

 a patient from their attack. Reference is made to 

 tuberculosis and pneumonia. The micro-organisms 

 which cause these two diseases lead all others as second- 

 ary invaders of the body, and undoubtedly cause a 

 larger number of deaths than all the diseases combined 

 to which they are secondary. Next to the tubercle 

 bacillus and the pneumococcus in point of frequency 

 as secondary invaders come the common pyogenic 

 or pus-producing bacteria, among which, it should 

 always be remembered, is included the microbe of 

 erysipelas. 



