AGENTS OF DISEASE 273 



marshy localities and the vicinity of stagnant 

 pools. These Anopheline mosquitos become 

 infected by biting a person who has the malarial 

 parasites in his blood, and, after a further life- 

 cycle of the parasite has been passed within their 

 stomachs, pass the parasites into the blood of 

 any healthy person they may subsequently feed 

 upon. It at once becomes obvious, therefore, 

 that a district in which these mosquitos are 

 present, only becomes malarious when a person 

 enters it who has the parasites in his blood ; and 

 that a country cannot become malarious unless 

 both these factors are present. 



In the history of the Island of Mauritius, 

 which prior to the year 1866 well deserved the 

 title of an earthly paradise, we have a most con- 

 vincing demonstration of the above facts. Prior 

 to 1866 this beautiful island had been a very 

 popular health resort for Anglo-Indians, many 

 of whom were malarial patients. Then, in an 

 evil hour for the island and its healthy inhabi- 

 tants, the Anopheline mosquito was by some 

 means introduced, and now malaria has become 

 endemic throughout the island. 



What the introduction of malaria into a 

 country means to its unfortunate inhabitants, is 

 brought home to us in the following quotation 

 from Sir Patrick Manson's " Lectures on Tropical 

 Diseases." " Imagine," he writes, " some district 

 in which Anopheline mosquitos abound, but 

 which is luckily free from malaria. A stranger 

 with parasites in his blood comes to the village 

 and is bitten by the local mosquitos, which thus 

 become infected and infective. The disease 



