74 IMMUNOLOGY 



EsTABiJSHMENT WiTiiiN TiiE TissuES. — Aftci' the iiivasioii of 

 the bodj^ surface (in trauma), it is necessary for the organisms 

 to establish themselves preparatory to dissemination elsewhere 

 in the body. Just how the pathogen establishes itself is un- 

 known. Wherry (1927) thinks that the bacteria or their prod- 

 ucts of growth cause hydration of the tissue and that this en- 

 ables them to grow and multiply. He calls attention to the fact 

 that there are found in filtrates of certain bacteria (e.g., C. 

 diphtheriae, Str. scarlatinac, Str. erysipilatis, CI. ivelchii, etc.) 

 substances which produce local congestion and edema (water in the 

 tissues). He suggests that the edematogenic substances may be 

 amines. His experimental approach is exceedingly interesting and 

 suggests that in the liydration of proteins the bacteria may have 

 a mechanism that enables them to grow and multiply. That the 

 mere production of edema is not always sufficient is suggested 

 by the lack of serious infection in many cases of extreme edema 

 of the lower extremities in women where the edema is caused by 

 the mechanical pressure of a large ovarian cyst in the abdomen. 

 This does not invalidate Wherry's conclusions that the hydration 

 of tissues by infectious agents aids in their groM^th and development. 



There are certain kinds of infectious agents such as the viruses, 

 rickettesia, and B. leprae that are intracellular parasites and re- 

 quire the presence of susceptible cells in which to multipl.y. Theo- 

 bald Smith (1933), and Goodpasture and Anderson (1937) have 

 emphasized the importance of hast-cell-parasite relationship in cer- 

 tain disea.ses. In their studies of experimental infections of the 

 chorio-allantoic membrane of chick embryos, Goodpasture and 

 Anderson (1937) found that many pathogenic bacteria find either 

 epithelial or mesodermal cells are both favorable and perliaps 

 nece.ssary media for the invasions of the living host. Their work 

 will be discussed more extensively in Chapter VII. 



Routes of Dissemination. — After infection is established there 

 are certain avenues of spread or routes of dissemination of the 

 infectious agent to be considered. The four avenues commonly 

 mentioned are surface spread, dissemination by way of the lym- 

 phatics (lympJiogenous) , blood stream {liematogenous) and direct 

 extension to adjacent tissues. The first of these can be illustrated 

 by infection of the nasopharynx. The infection may extend down- 

 ward over the mucous membrane to the tonsil, trachea, and lungs 



