INFECTION AND RESISTANCE 13 



diseases may produce marked local manifestations and rapidly in- 

 vade the blood stream, as is true of typhoid fever. This organism 

 enters the lymph-nodes of the intestinal tract, produces enlarge- 

 ment, softening, and necrosis. The diarrhoea in these cases is largely 

 if not wholly due to the local lesions, but the severe general mani- 

 festations are due principally to the entrance of the organisms into 

 the blood stream. Other diseases may show little local manifesta- 

 tion, as is true of tetanus, but even with slight local disturbances 

 profound general symptoms occur as the result of absorption of 

 toxin. Other diseases, such as anthrax, may show little local mani- 

 festation, but rapidly exhibit generalized infection through the blood 

 stream. Infection then simply signifies successful invasion. Bac- 

 teremia signifies the presence of organisms in the blood. Septicemia 

 signifies blood infection associated with the production of toxic 

 substances. Pyemia indicates that bacteria are present in the blood 

 stream and because of lodgment in numerous situations produce 

 multiple abscesses. Sapremia indicates absorption of toxic products 

 from the growth of saprophytic organisms. Primary infections are 

 those which occur without any decrease of resistance due to another 

 infection. Secondary infections occur in individuals already suffer- 

 ing from an infection of another nature. Such an infection is well 

 exemplified in the secondary infection of a tuberculous cavity of the 

 lung by staphylococcus. Terminal infections are those which occur 

 near the fatal termination of some other disease, whether that other 

 disease be of bacterial nature or of some other origin. Infections of 

 this type are seen in the terminal broncho-pneumonias and sep- 

 ticemias which occur in the course of certain chronic diseases. 

 Mixed or multiple infections are not rare and it is sometimes diffi- 

 cult to determine which infection is of greater importance. There is no 

 doubt that one infection influences another existing at the same time and 

 usually in a manner deleterious to the patient. Infection with measles or 

 lobar pneumonia may excite latent tuberculosis into activity. Duke 

 reports the lighting up of latent syphilis by an attack of typhoid 

 fever and of latent gonorrhea by an attack of tonsillitis. The re- 

 moval of one chronic infection may favorably influence another, as 

 seen in the relief of certain cases of pyorrhea alveolaris by the re- 

 moval of infected tonsils and in numerous other instances of mul- 

 tiple chronic infections. 



Factors Favoring the Invader. The small size of pathogenic 

 bacteria and protozoa aids in their avoidance of detection, favors 

 transportation, and aids in penetration. The rapidity of multiplica- 

 tion of such organisms is of considerable importance to their patho- 

 genic powers. Those bacteria which form spores resist destructive 

 agents and can resume activity when favorable conditions present. 

 Certain of the protozoa, more particularly the endamebae, are cap- 

 able of forming cysts which are more resistant to unfavorable en- 

 vironment than the active organism. Either in the active state or 

 in the vegetative state, organisms may persist for a long time in the 

 so-called carriers, in intermediate hosts, or living as saprophytes. 



