238 PATHOGENIC BACTERIA OUTSIDE THE BODY 



accumulating which may place these diseases in the next 

 class. Anthrax is considered in some instances to be trans- 

 mitted by flies and by vultures in the southern United States. 

 Transmission of typhoid, dysentery, cholera and other 

 diseases by flies is well established in man. Why not hog 

 cholera from farm to farm by flies, English sparrows, pigeons 

 feeding or by turkey buzzards? Though this would not 

 be easy to prove, it seems reasonable. 



Preventing contact of such animals with the discharges 

 or with the carcasses of those dead of the disease, destruc- 

 tion of insect carriers, screening and prevention of fly breed- 

 ing are obvious protective measures. 



{e) In this class come certain diseases for which particu- 

 lar insects are necessary for the parasite in question, so that 

 certain stages in its life history may be passed therein. The 

 surest means for eradicating such diseases is the destruction 

 of the insects concerned. Up to the present no bacterial 

 disease is known in which this condition exists, unless Rocky 

 Mountain spotted fever and typhus fever shall prove to 

 be due to bacteria. Such diseases are all due to protozoa. 

 Among them are Texas fever due to Piroplasma higeminum 

 in this country, which has been eradicated in entire districts 

 by destruction of the cattle tick {Margaropus annulatus). 



Piroplasmoses in South Africa among cattle and horses 

 and in other countries are transmitted in similar ways. 

 Probably many of the diseases due to spirochetes and trypan- 

 osomes are likewise transmitted by necessary insect inter- 

 mediaries. In human medicine the eradication of yellow 

 fever from Panama and Cuba is due to successful warfare 

 against a certain mosquito (Aedes). So the freeing of 

 large areas in different parts of the world from malaria 

 follows the destruction of the mosquitoes. The prevention 

 of typhus fever and of trench fever by ''delousing" methods 

 is familiar from recent army experience though for typhus 

 this method had been practised in Russia for more than ten 

 years to the author's personal knowledge. The campaign 

 against disease in animals and man from insect sources 

 must be considered as still in its infancy. The full utiliza- 

 tion of tropical lands depends largely on the solution of this 

 problem. 



