98 INFECTION AND IMMUNITY. 



start a disposition to remain localized, although in 

 the end they may involve various organs, by means 

 of metastases, and in some of them a more or less 

 continuous blood infection may arise. Such dis- 

 eases are tuberculosis, actinomycosis, blastomyco- 

 sis (oidiomycosis), rhinoscleroma, sporotrichosis, 

 and perhaps leprosy. They are characterized by 

 the formation of a good deal of fibrous tissue, 

 which tends to limit rapid extension by the forma- 

 tion of metastases, and by a disposition to invade 

 contiguous tissues. New foci may be set up in 

 distant organs by means of metastasis, the blood- 

 stream in the meantime being comparatively free 

 from living micro-organisms. A true septicemic 

 condition may be produced in tuberculosis by the 

 sudden pouring of large quantities of bacilli into 

 the circulation from a cheesy focus which has 

 ruptured into a vessel. This again results in the 

 formation of many minute foci in various parts 

 of the body (diffuse miliary tuberculosis). The 

 conditions are similar in blastomycosis, leprosy 

 and glanders. Earely metastatic infection with 

 actinomyces is found. 



These chronic infections are not the only ones, 

 however, in which new foci may originate by 

 metastasis. A streptococcus infection of the heart 

 valves, or an infected thrombus in some vein, cause 

 "pyemic" abscesses in various organs when infected 

 clots from the original site are set free in the circu- 

 lation. The foci of infection found in the kidney in 

 typhoid fever, and the involvement of the joints 

 in gonorrhea, are further examples of metastatic 

 invasion. 



Sc s 5 steSiic ^ s a l rea( ty indicated, systemic infection may 

 infections, take place in a secondary and accidental way in 



