MODES OF BACTERIAL ACTION 179 



this disease, and are of a severe character. It is not uncommon 

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

 wasting disease, collections of uiicrococci 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 lust 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 

 dc-MTibed 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 tin- body, and (6) the production by them of poisons 

 \\hirh 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. Inflation 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 pneunio- 

 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 

 }><>.<t 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 pa<s by the lymph or blood stream toother parts or 

 organs in which they settle, multiply, and produce lesions, as in 

 tubercle. 



L'. /'/'"/////"// of CJwmical Poisons. In all these cases the 

 growth of the organisms is accompanied by the formation of 



