PARASITISM AND PATHOGENESIS 207 



due to disturbance in function of the local tissue, such as laryngeal 

 obstruction in diphtheria, or to the absorption into the lymph 

 and blood of poisons produced at the infected site. Such ab- 

 sorption results in toxemia with symptoms due to poisoning of 

 distant tissue elements. On the other hand, the infectious 

 agent may pass quickly to the blood stream, without appreciable 

 local reaction and multiply there, as in malaria, trypanosomiasis 

 and streptococcus bacteremia. Again there may first develop 

 an intense local reaction, with subsequent extension to the 

 blood stream with fatal issue, as in malignant pustule (anthrax). 

 In other instances repeated temporary invasions of the blood 

 occur, with numerous localized abscesses in various parts of 

 the body, a condition to which the name pyemia has been applied. 

 Of particular interest are those general infections of the blood 

 stream, which finally fade away, but leave behind localized 

 . infections in the joints, on the heart valves, in the central nervous 

 system, or other parts of the body. Sleeping sickness, syphilis, 

 acute articular rheumatism and generalized gonococcus infection 

 belong in this category. 



Transmission of Infection. — The manner in which an infectious 

 agent passes from its host to a new victim varies considerably. 

 In general it may l^e said to occur (i) by direct contact or close 

 association, transmission by contagion, (2) through the agency of 

 intermediate dead objects as passive carriers, transmission by 

 Jomites, or (3) through the agency of a living or dead object, in 

 which the parasite undergoes development or multiplication, 

 transmission by miasm. These terms have been employed in 

 the past to designate rather hypothetical objects not to say 

 abstract ideas, and their application to the facts learned by 

 modern research is, perhaps, not desirable. Nevertheless, they 

 may be made to fit the observed phenomena in a way. Thus, 

 syphilis and gonorrhea are transmitted by contagion; diphtheria 

 and small-pox by contagion and by fomites, tetanus and anthrax 

 by fomites and perhaps also miasm ; plague by contagion, fomites 

 and miasm (through the rat and flea); malaria, trypanosomiasis 



