TYPHUS FEVER 109 



appeared, but in Ireland and in Brittany it still 

 lingers endemic, that is, sporadic cases occur which 

 are not due to the immigration of an infected 

 person, but which show that all the essentials 

 for the disease are constantly present. These 

 essentials are, firstly, the presence of lice, and 

 secondly, the actual causative agent of the 

 disease, whatever that may be, lingering either 

 in the lice or in the bodies of those who have once 

 suffered from the malady. To develop an epi- 

 demic from these sporadic cases, conditions of 

 unclean living and poor housing, together with a 

 general infestation of lice among the population, 

 are essential. The disease is one which is mainly 

 confined to cold and temperate climates, and 

 those parts of the Tropics where the heat is not 

 intense. In a country such as Mexico the 

 epidemics occur on the hills and not in the hot 

 low-lying coast towns. Similarly in temperate 

 countries the epidemics rage more fiercely in 

 the winter than in the summer. With the ex- 

 ceptions mentioned, typhus has been recorded 

 from the greater part of the world, though 

 Australasia, with the exception of the Celebes 

 Islands, appears to have been spared its ravages. 

 Outbreaks of the disease have not always been 

 recognised as such, probably because the char- 

 acteristic rash is not obvious on dark skins, and 

 also because diagnosis must rest on symptoms, 

 since modern methods in medicine have failed 

 to find a means of recognising the complaint 



