MODES OF BACTERIAL ACTION. 127 



involved, namely, in the first place, the multiplication of 

 the living organisms after they have entered the body, and, 

 in the second place, the production by them of poisons 

 which may act both upon the tissues around and upon the 

 body generally. The former corresponds to infection, the 

 latter is of the nature of intoxication or poisoning. In 

 different diseases one of these is usually the more prominent 

 feature, but in all, both are more or less concerned. 



1. Infection and Distribution of the Bacteria in the 

 Body. After pathogenic bacteria have invaded the tissues, 

 or in other words after infection by bacteria has taken 

 place, their further behaviour varies greatly in differen 

 cases. In the lower animals various forms of septicae 

 may be produced, attended by an extensive multiplicati 

 of the organisms in the blood throughout the body 

 example, the septicaemia produced by the pneumococcus 

 in rabbits), but in septicaemia in man, the multiplication 

 very seldom, if ever, occurs to so great a degree. For 

 though the organisms may enter the blood stream and are 

 carried by it to various organs, they rarely remain in large 

 numbers in the circulating blood, and their detection in it 

 during life by microscopic examination, and even by 

 culture methods, is rare. In such cases, however, the 

 organisms may be found post mortem lying in large numbers 

 within the capillaries of various organs, e.g., in cases of 

 septicaemia produced by streptococci. (Relapsing fever 

 forms an exception, as in it numerous organisms may be 

 seen in a drop of blood.) In the human subject usually 

 one of two things happens. In the first place, the organ- 

 isms may remain local, producing little reaction around 

 them, as in tetanus, or a well-marked lesion, as in diph- 

 theria. Or in the second place, they may pass by the 

 lymph or blood stream to other parts or organs in which 

 they settle, multiply, and produce lesions, as in tubercle. 



2. Production of Chemical Poisons. In all these cases 

 the growth of the organisms is accompanied by the form- 

 ation of chemical products, which act generally or locally 

 to a greater or less extent as toxic substances. The toxic 



