78 THE ECOLOGY OF ANIMALS 



Ship transport was never fast enough for a person 

 to reach a distant country while still in the stage at 

 which mosquitoes can obtain the virus from the 

 peripheral blood. Air travel makes this possible, 

 and it is suggested that yellow fever might actually 

 get to Asia, where the appropriate type of mosquito 

 already exists naturally. This example illustrates 

 the extreme dangers that modern transport engineer- 

 ing triumphs have introduced into the field of 

 economic ecology. 



Economic problems which come into the realm of 

 ecology are to be found in thousands. They include 

 the following main categories : diseases of man and 

 of domestic animals ; pests of agriculture and stored 

 products and forestry ; fisheries — including whale 

 fisheries ; conservation of mammals and birds — 

 including the fur trade and game research. These 

 are the main categories, but there are others which 

 have great importance in their own spheres. And, 

 of course, the future of ecology as the accurate study 

 of natural history and in relation to our general 

 outlook upon wild animal life, is entitled to be con- 

 sidered as an important educational element. 



Diseases of man have a special interest owing to 

 the life histories of many parasites that have alternate 

 hosts. Bubonic plague (sometimes spreading widely 

 among human beings by direct breath infection as 

 pneumonic plague) arises in all cases from rodents. 

 These may be either ' domestic ' rats, or on the other 

 hand may be marmots (Mongolia), susliks— a smaller 

 marmot — (Russia), gerbilles (South Africa), ground 

 squirrels (California), or guinea-pigs (Ecuador), or 

 other forms (Wu Lien Teh and Pollitzer, 1926). 

 The original contact between man and rodent is by 

 fleas which carry the Bacillus pestis. Tularaemia is 

 a fairly recently studied disease which also comes 

 from rodents, either by contact with their dead 

 bodies, or by the bites of insects such as Tabanid 

 flies or by the bite of a tick. Tt occurs in North 



