390 APPLICATION OF METHODS OF BACTERIOLOGY 



essential features of this riddle, we must bear in mind several 

 fundamental facts : 



1. That pneumonia is not invariably the consequence of 

 the presence of pneumococci upon the mucous surfaces or 

 in the body, for that organism is often found, fully virulent 

 in the mouth, nose or upper air passages of persons in perfect 

 health. 



2. That pneumonia, when not terminating fatally, is a 

 self -limited disease, i. e., the signs and symptoms increase 

 from the start until a point is reached, "the crisis," when 

 their severity suddenly begins to lessen and may continue 

 to do so until recovery is established. 



3. That up to, and for a time after the crisis, often far 

 into convalescence, living virulent pneumococci are present 

 in the lungs. They can be found constantly in the sputum 

 and often in smaller or larger numbers in the circulating 

 blood. Their number seems at times to be affected little, 

 if at all, by the forces that occasion the crisis. 



4. That the pathogenic activities of the pneumococcus are 

 not referable to an extracellular toxin, properly so called, 

 but rather to an endotoxic component that is liberated 

 in the body when the bacteria are disintegrated and that 

 may be liberated artificially by certain solvents and under 

 such conditions as favor autolysis, i. e., by the self-digestion 

 of the bacteria. 



5. That in the blood of convalescents from pneumonia 

 specific, protective antibodies are to be found, but as they 

 are inconstant both as to their presence and as to their 

 amounts it is impossible to decide their role in the mechanism 

 of recovery. 



6. That animals may be actively immunized from pneu- 

 mococcus infection with but little difficulty, but the serum 



