MODES OF BACTERIAL ACTION 185 



bacterial infection is seen in the case of diabetes ; tuberculosis 

 and infection with pyogenic organisms are prone to occur in this 

 disease, and are apt to be of a severe character. It is not 

 uncommon to find in the bodies of those who have died from 

 chronic wasting disease, collections of micrococci or bacilli in the 

 capillaries of various organs, which have entered in the later 

 hours of life that is to say, the bacterium- free condition of 

 the blood has been lost in the period of prostration preceding 

 death. 



The methods by which the natural resistance may be speci- 

 fically increased belong to the subject of immunity, and are 

 described in the chapter on that subject. 



Modes of Bacterial Action. In the production of disease by 

 micro-organisms there are two main factors involved, namely, 

 (a) the multiplication of the living organisms after they have 

 entered the body, and (b) 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 both are 

 always 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 different cases. In certain cases 

 they may reach and multiply in the blood stream, producing a 

 fatal septicaemia. In the lower animals this multiplication of 

 the organisms in the blood throughout the body may be very 

 extensive (for example, the septicaemia produced by the pneumo- 

 coccus in rabbits) ; but in septicaemia in man it very seldom, if 

 ever, occurs to so great a degree, the organisms rarely remain 

 in large numbers in the circulating blood, and their detection in 

 it during life by microscopic examination is rare, and even culture 

 methods may give negative results unless a large amount of blood 

 is used. 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 strepto- 

 cocci. In the human subject more frequently one of two things 

 happens. In the first place, the organisms may remain local, 

 producing little reaction around them, as in tetanus, or a well- 

 marked lesion, as in diphtheria, etc. 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. 



