155 



piirel}' saprophytic in their functions they can become 

 pathogenic or disease producing. 



Now since the bacilli or their spores are so 

 plentiful in the mote dust of the air, we cannot 

 wonder that they abound in our houses, on our 

 clothes, on our persons, and of course on our food. 

 And seeing that in addition to their being saprophytes 

 the}' are also " facultative parasites," or as I have 

 explained, capable under favouring conditions of 

 producing disease, we must ask ourselves why it is 

 that our birds, as well as their owners, are not 

 universall}^ destroyed. The fact of the matter is that 

 there is a constantly existing and never ending battle 

 going on. So long as the animal is above par, so long 

 as those cells of his body, whose special duty it is to 

 repel the attacks of microbic invaders, are main- 

 tained in a state of vigour, the victory remains with 

 the attacked. And this is what generally happens, 

 especially when the invading microbe is only of an 

 average degree of power and virulence. But let the 

 defending cells — the phagoc3^tes — from any cause 

 whatever once falter in their attempts to repulse the 

 eneni}', then defeat is sure to follow in the shape of 

 disease. If this can occasionally happen when the 

 bacillus is onl}^ of average power and malignancy 

 what are we to expect when it has been generated 

 under conditions that raise its virulence to the 

 highest pitch, and when while invading the bodies of 

 our birds, it is supplied with the pabulum which most 

 of all tends to keep it up to the highest state of 

 fighting efficiency? Under such circumstances the 

 result can only be to sooner or later wear out the 

 defenders, however strong and watchful they may 

 have been at the beginning of the fight, and to give 

 over a conquered system to the remorseless sway of 

 the victorious foe. 



(To be continued.) 



