114 



INFECTION AND IMMUNITY. 



Mechanical 

 Injuries. 



Fibrin. 



Connective 

 Tissue. 



Malaria. 



produce profound disturbances in metabolism and 

 nutrition by interference with the functions of 

 organs. It is not the intention, however, to enter 

 into a discussion of these obscure influences. 



The mechanical injuries which micro-organisms 

 cause are, at least in most cases, the result of a 

 previous toxic action, i. e., they are secondary 

 effects. This is true of the emboli, consisting of a 

 mixture of fibrin, cells and micro-organisms, which 

 arise in a valvular endocarditis, and of thrombi 

 which are formed in vessels as a consequence of 

 infection. 



In lobar pneumonia we have a good example of a 

 mechanical disturbance of importance. The alveoli 

 become filled with a fibrinous and purulent exudate 

 which makes a large area of pulmonary tissue 

 unavailable for respiration. Yet, even here, the 

 mechanical disturbance has arisen only as a result 

 of the toxic action of the pneumococcus on the 

 capillary walls and the alveolar epithelium, per- 

 mitting the escape of the blood and serum. 



Some chronic infections are characterized by the 

 development of new connective tissue and vessels; 

 this is seen especially in syphilis, tuberculosis and 

 actinomycosis. The import of the new connective 

 tissue depends on its location. A large amount of 

 it may form in pre-existing fibrous tissues with no 

 consequent harm; but even a small scar, gumma 

 or tubercle in the brain, or deformities of the heart 

 valves which follow inflammation, may cause 

 serious results. 



A genuine direct mechanical disturbance appears 

 to be caused by the malarial organisms in that 

 they occasionally accumulate in the capillaries of 

 the intestines and brain in such numbers as to 



