INFECTION IN PNEUMONIA. 507 



bronchi, may be carried through the walls of the 

 latter, perhaps by the leucocytes, and reach the 

 alveoli directly through the lymph channels or 

 after having caused infection in the peribronchial 

 lymph glands. Others express the opinion that 

 pneumonia follows blood infection in many or 

 most instances, i. e., that the infection is hemato- 

 genous, the cocci having reached the blood in some 

 obscure manner. That the infection may be hem- 

 atogenous is shown by the occasional occurrence of 

 pneumonia secondary to pneumococcus infection in 

 other parts of the body. 



Knowing the fairly constant presence of pneu- conditions 



. . .. * . ,1 for Infection. 



mococci in the upper respiratory passages m the 

 normal individual, it seems certain that some un- 

 usual condition must arise to precipitate infection 

 of the pulmonary tissue. Concerning the nature 

 of these conditions, we have little but theories. 

 They may rest either with the microbe or the in- 

 dividual, or with both. The pneumococci which 

 are normally on the mucous surfaces may undergo 

 an increase in virulence, or more virulent organ- 

 isms from the outer world, or from pneumonic pa- 

 tients, may be inhaled. The latter condition is an 

 important one in relation to the contagiousness of 

 pneumonia and the development of epidemics. 

 Park and Williams found a larger percentage of 

 virulent organisms in the sputum of pneumonics 

 than in that of normal persons. It is possible that 

 the pneumococcus in being passed from one patient 

 to another undergoes an increase in virulence, sim- 

 ilar to the increase which may be obtained by pass- 

 ing bacteria through animals. 



On the other hand, it is very probable that es- Decrease of 

 sential changes take place in the individual, Resistance - 



