66 Causes of Disease. 



secondary metastatic foci of infection, are caused, or the micro- 

 organisms are widely disseminated throughout the whole body 

 {general infection, hactericcmia). As an illustration, streptococci of 

 epidemic coryza in the horse gain access to the pharynx with the 

 drinking water or with the inspired air ; they here first give rise to 

 a purulent catarrhal inflammation, penetrate by direct growth into 

 the pharyngeal follicles, gradually make their way along the 

 Eustachian tubes to the middle ear and here set up a similar puru- 

 lent inflammation. Being carried away by the lymph current and 

 by leucocytes, they give rise to abscess formation in the retro- 

 pharyngeal lymph glands, and by going lower, in the cervical nodes ; 

 and, too, they may be swallowed and infect the mesenteric lymph 

 glands as they pass along the chyliferous tract. Passing from, the 

 lymph glands to finally reach the blood, they are disseminated by 

 the latter generally throughout the body, and cause a variable num- 

 ber of metastatic abscesses in such situations as the brain, lungs, 

 liver and kidneys, eventually a septico-pysemia. In similar way 

 infection of the umbilical vein in the new-born by pyogenic bacteria 

 causes primarily a local abscess-formation at the umbilicus, fol- 

 lowed by multiple venous-embolic abscesses in the liver, later in the 

 lungs, the joints and elsewhere. 



It may happen that at the point of infection the local lesions 

 are so slight as to be appreciable only by microscopic study, that 

 the microbe passing from this point first lodges in the lymph 

 glands or may perhaps even pass through several lymph-nodes 

 without occasioning any disturbances, multiplying and manifesting 

 its influences only after- it has gained access to the blood and 

 circulated in the body and become fixed in this or that position 

 at a distance from the original site of entrance. The tubercle 

 bacillus, for example, may be absorbed from the intestines with- 

 out causing any alterations in them, but giving rise to caseation 

 of the mesenteric lymph-nodes ; or these may be traversed by it, 

 the germ gaining access to the blood, and perhaps first deposited 

 in the bone-marrow, where it gives origin to the primary tubercu- 

 lous focus. 



The physiological movements and changes of position of the 

 intestines and muscles aid in great measure the spread and dis- 

 tribution of the invading and multiplying microorganisms : 

 pyogenic microbes which have gained access to the peritoneal 

 cavity are apt to be spread over the whole peritoneal sur- 

 face by the peristaltic movement of the intestine, the resulting peri- 



