38 INFECTION AND IMMUNITY. 



not it is discharged in such manner that it is read* 

 ily disseminated. Some of these points are con- 

 sidered in following chapters. 



Relation of As a general principle it may be stated that 



re |ite of when the surfaces of the body are the seat of infec- 



invoivement. ^ Qn ^ e m i cro _ or g an i snis are discharged into the 



outer world more or less easily. This applies not 

 only to the cutaneous surface, but also to the mu- 

 cous surfaces, as the lungs, alimentary tract, gall- 

 bladder, and urinary bladder, and also to discharg- 

 ing sinuses and abscesses which rupture through a 

 cutaneous or mucous surface. The surfaces ma^ 

 be involved either primarily, as in tuberculosis or 

 blastomycosis of the skin, or as a part of a gener- 

 alized infection, as in the case of some of the 

 eruptive diseases. Thus from the respiratory pas- 

 sages the microbes of pneumonia, tuberculosis, 

 diphtheria, tonsillitis caused by other micro-organ- 

 isms, plague pneumonia, influenza, whooping- 

 cough, epidemic cerebrospinal meningitis and 

 probably measles, scarlet fever and smallpox, are 

 discharged into the surrounding air. From the 

 intestinal tract the micro-organisms of tubercu- 

 losis, typhoid fever, cholera and of other less im- 

 portant diseases reach the outer world. From the 

 genito-urinary tract, those of gonorrhea, syphilis, 

 tuberculosis, typhoid and paratyphoid fevers ; from 

 the skin the microbes of ulcerative processes, the 

 contagious dermatoses, trichophytosis, favus, etc., 

 and probably some of the contagions exanthemata 

 (scarlet fever, measles, etc.). 



Metastatic Of great importance is the fact that some infec- 

 tions which are primarily systemic, or become so 

 during the course of infection, commonly involve 

 some excreting organ secondarily, thus rendering 



