THE PATHS OF PYOGENIC INFECTION. 163 



others the kidneys (Fig. 46), in others the bones or joints, 

 and so on. The term cryptogenetic has been applied by 

 some writers to such cases in which the original point of 

 infection cannot be found, but its use is scarcely necessary. 



In cases of typical pyaemia originating from aseptic wound, 

 the infection of the blood usually takes place by the occur- 

 rence of a septic phlebitis of one of the adjacent veins with 

 formation of a thrombus. The thrombus is invaded by the 

 organisms, softens, and gives rise to emboli, which emboli, 

 bearing the organisms with them, are arrested in the organs 

 to which they are carried first, generally the lungs, and set 

 up in them secondary abscesses which may reach a con- 

 siderable size. Thence other organs may be affected in a 

 corresponding manner. In such cases some of the pyogenic 

 organisms mentioned, most frequently staphylococci and 

 streptococci, are often associated with the organisms of 

 putrefaction. Cases in which the organisms are carried in 

 this way should be distinguished from those in which the 

 organisms are free in the blood stream and settle in the 

 parts specially susceptible, though in some instances both 

 methods of infection may be present together. 



The paths of secondary infection may be conveniently 

 summarised thus : First, by lymphatics. In this way the 

 lymphatic glands may be infected, and also serous sacs in 

 relation to the organs where the primary lesion exists. 

 Second, by natural channels, such as the ureters and the 

 bile ducts, the spread being generally associated with an 

 inflammatory condition of the lining epithelium. In this 

 way the kidneys and liver respectively may be infected. 

 Third, by the blood vessels : (a) by a few organisms gaining 

 entrance to the blood from a local lesion, and settling in a 

 favourable nidus or a damaged tissue, the original path of 

 infection often being obscure ; (<) by a septic phlebitis with 

 suppurative softening of the thrombus and resulting embol- 

 ism ; and we may add (c) by a direct extension along a 

 vein, producing a spreading thrombosis and suppuration 

 within the vein. In this way suppuration may spread along 

 the portal vein to the liver from a lesion in the alimentary 



