-xvii.] SEPTIC AND PATHOGENIC ORGANISMS. 167 



above morbid processes possess this pathogenic power db initio, 

 not due to any peculiar condition of growth. 



Amongst the legion of different species of micrococci and 

 bacilli occurring in putrid substances, the great majority are 

 quite harmless ; when introduced into the body of an animal 

 they are unable to grow arid to multiply, and therefore are 

 unable to produce any disturbance. But some few species 

 there are which, although ordinarily growing and thriving in 

 putrid substances, possess this power, that when introduced 

 into the body of a suitable animal they set up here a specific 

 disease. 



One of the best studied cases is that of the bacillus anthracis. 

 This organism is capable of growing well and copiously out- 

 side the body of an animal, it thrives well wherever it finds 

 the necessary conditions of temperature, moisture, and nitro- 

 genous material ; when it finds access into the body of a 

 suitable animal it produces the highly infectious fatal malady 

 known as anthrax. The micrococcus of erysipelas is now well 

 known through the admirable researches of Fehleisen to be 

 capable of existence and multiplication outside the animal 

 body ; it grows well in artificial cultures, so does the tubercle 

 bacillus of Koch, so does the bacillus which I described of 

 swine-plague, mentioned in a former chapter, and so do other 

 micro-organisms. Davaine's septicaemia in rabbits, Koch's 

 septicaemia in mice, &c., &c., cannot be produced by every 

 putrid blood or putrid organic fluid, only by some, only now 

 and then, i.e. when the particular micro-organism capable of 

 inducing the disease is present in those substances, and then 

 only when it finds access into a suitable animal. Davaine's 

 septicaemia of rabbits cannot be induced in guinea-pigs, Koch's 

 septicaemia of mice cannot be induced in guinea-pigs, anthrax 

 bacilli cannot induce the disease in dogs, and so with the other 

 micro-organisms. 



We conclude then from this that some definite micro- 

 organisms, although as a rule existing and growing in various 

 substances of the outside world, have the power when finding 

 access into the body of a suitable animal to grow and thrive 

 here also, and to induce a definite pathological condition. But 

 this power they have ab initio. Those that do not possess this 

 power cannot acquire it by any means whatever. Just as there 

 are species of plants which act as poisons to the animal body, 

 and other species of plants which, although belonging to 

 the same group and family, and although very much alike to 

 the others, have no such power and cannot acquire such a 

 power by any means, so there are micro-organisms which 



