PUBLIC HEALTH 



29 



are strictly human parasites and do not occur upon any other 

 animals. Only the body louse appears to act as a carrier of 

 the louse-borne diseases. 



Typhus fever has been well known for many years and re- 

 garded as a disease characteristic of filthy surroundings. 



Fig. 12. The body louse (Pediculus corporis). 



During our own civil war it claimed many victims among 

 the inmates of army prisons, and has been endemic though not 

 very prevalent in many ])arts of the world in times of peace 

 (Figs. 13a & 13b). Through the researches of Ricketts and 

 others we know that typhus is spread by the body louse and 

 its epidemiology is at once made clear. When it broke out in 

 Serbia in 1915 in severe epidemic form, a knowledge of the 

 method of its transmission made control possible, even under 

 extremely difficult and unfavorable circumstances. 



Trench fever has attracted notice in the P^uropean war 

 zones, to which it appears to be restricted so far as present 

 knowledge extends. That it is a new disease is, however, 



