14 PLANT DISEASE 



quantity of debris is retained in the system 

 of an animal suffering from acute anaemia. 



It follows that the food of these bacteria 

 increases as the blood degenerates, and it is 

 clear that they will increase more rapidly 

 in those animals where the conditions are 

 favourable to their growth, than in those where 

 there is but a scanty supply of the food on 

 which they thrive. To this may be attributed 

 the variation in the virulence with which a 

 given disease attacks different animals, some 

 being by their physical condition a more fer- 

 tile soil than others for the propagation of the 

 pathogenic bacteria. 



We may take as an illustration tuberculosis, 

 where some cases linger on for seven or eight 

 years and others die in as many weeks. 



The greater the quantity of oxygen and the 

 less the quantity of debris in any individual, 

 the greater the immunity, while the converse 

 condition provides us with the more acute 

 forms of the disease. 



But variation in these two factors does not 

 cover the entire ground in relation to immunity 

 or susceptibility in disease, for it is recognized 

 that proteids are fatal to pathogenic bacteria. 



