CAUSES OF DISEASE. 33 



their home in the ground. The bacteria that produce 

 pus (pyogenic bacteria) are also found in the ground. 



Insects, such as flies, bed-bugs, mosquitoes, etc., 

 may be the means of conveying infections. Finally, 

 persons may convey infections. Among persons con- 

 veying infections, physicians and nurses are especially 

 dangerous on account of the frequent and close contact 

 that they have with the sick. 



The manner in which complications have heretofore 

 been spoken of places them in the same category with 

 secondary infections. This conception of them, how- 

 ever, requires qualification. Besides resulting from 

 invasion of the body by bacteria other than the one 

 producing the original infection, complications may be 

 due to another localization in a distant part of the body 

 of the same organism that produced the original infec- 

 tion. Under such circumstances we do not speak of 

 the complication as a secondary infection, but a second- 

 ary localization or metastasis. Ignorance of the nature of 

 infectious agents and their migratory tendency led, in the 

 past, to such names as typhoid-pneumonia, a designation 

 which is no longer countenanced because we know that 

 this disease, even when the pneumonia accompanies or 

 initiates typhoid, is typhoid fever with pulmonary locali- 

 zation of the typhoid bacillus in the lungs. Misconcep- 

 tions concerning their origin were likewise responsible 

 for such names as typho-malarial fever, diphtheritic 

 tonsillitis, etc., hybrids for which there is no excuse. 

 3 



