BACTERIA IN DISEASE. 165 



In this connection it is proper to refer to certain diseases 

 due to animal microorganisms. Malaria is conveyed from 

 man to man by mosquitoes of the genus Anopheles, and 

 is probably transmitted exclusively in this manner. The 

 parasite of malaria undergoes part of its cycle of develop- 

 ment in man, and another part in the mosquito. Similarly, 

 in Texas Fever, a disease of cattle, it has been shown by 

 T. Smith that the parasite (a protozoon, Piroplasma) passes 

 from cow to cow through the cattle-tick (Boophilus annul- 

 atus or bovis). 1 In surra, a disease chiefly affecting horses, 

 and in the tsetse-fly disease of animals the parasite (a proto- 

 zoon, Trypanosoma ) , is transmitted by the bites of flies. 2 

 It has recently been shown that the infectious agent of 

 yellow fever may be introduced into man by mosquitoes of 

 the genus Stegomyia. Under the administration of the 

 United States Army yellow fever was suppressed in Havana 

 chiefly by measures intended to prevent the disease from 

 being carried by mosquitoes. 3 



Auto-Infection. It is possible for the bacteria of disease 

 to be derived from the individual's own body auto-infec- 

 tion. The microbes of lobar pneumonia, for instance, 

 flourish in the mouths of a large number of people. The 

 bacillus coli communis, which constantly inhabits the in- 

 testines, may invade other organs and exhibit pathogenic 

 properties when the way is opened up for it by other dis- 

 ease processes. 



Bodily Conditions that Dispose to Infection. The de- 

 velopment of an infectious disease may be favored by cer- 

 tain bodily conditions. Hunger, cold and exhaustion make 

 the body more liable to the inroads of pathogenic bacteria ; 

 so also do anemia and chronic diseases. Those suffering 

 from diabetes, as is well known, are especially liable to 



1 See V. A. Moore, " Infectious Diseases of Animals," 1902. 



2 Report on Surra, U. S. Bureau Animal Industry, 1902. 



3 Carroll, Journal American Medical Association, May 23, 1903. 



