clbc Srorv) of Bii^-Bcatb. 



By \V. Gko. Cresweix, M.D., L.R.C.P., F.Z.S. 

 ("Continued from page iSy). 



y'^ AViXG dealt with the part phayed in the pro- 

 l-^ duction of septicseiiiia by the conditions under 

 ,-jL/ which the virulence of the bacillus is increased, 

 and having discovered that bacilli propagated 

 at a low temperature are not so powerful for harm as 

 those which have been developed at high temperatures 

 with egg yelk for a nidus, it now remains ior us to 

 consider those influences which are inherent in the 

 birds themselves and which are of so much importance 

 in connection with the same process. I allude, of 

 course, to the varN'ing degrees of receptivity of the 

 disease on the one hand and to those of immunity 

 against it on the other hand, which are found to exist 

 in different species and in different individuals. 



This is naturally a difficult subject on which to 

 discourse clearly to those who have never paid any 

 attention to biological problems. It is so wide in its 

 scope, and there are so many factors to be reckoned 

 with, that at first I thought of leaving it alone 

 altogether and of contenting myself with \\\y previous 

 meagre allusions to " strong and healthy birds," and to 

 " temporarily diminished power of resistance " as 

 occurring in individuals. But judging from the tone 

 of many letters I have received, I am so conscious of 

 the why and wherefore attitude cropping up among 

 my readers, that I am constrained to devote at least a 

 few lines to the question. 



