XVIL] SEPTIC AND PATHOGENIC ORGANISMS. 229 



micrococci being present in the blood-vessels. Further, a 

 progressive necrosis in mice by inoculating them with putrid 

 fluids, the necrosis being due to the growth of micrococci 

 and spreading from the seat of inoculation, and destroying 

 as they spread all the elements of the tissue. All these 

 cases have been minutely described by Koch in his 

 classical work, Die Aetiologie der Wundinfectionskrank- 

 heiten, Leipzig, 1879. I have in addition mentioned in 

 Chapter VII. 13 a micrococcus causing abscess and 

 pyaemia in mice. 



Now do these cases prove that septic micro-organisms, 

 living and thriving in putrid organic fluids, can, when intro- 

 duced into the body of animals, owing to some peculiar 

 unknown condition, so change as to produce a fatal infections 

 disease? I must say, with Koch, who has very ably 

 discussed all these points, ' No.' Those organisms which 

 are connected with the above morbid processes possess this 

 pathogenic power ab 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 and 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 an- 

 thracis. This organism is capable of growing well and 

 copiously outside the body of an animal, it thrives well 

 wherever it finds the necessary conditions of temperature, 

 moisture, and nitrogenous material ; when it finds access to 



