CHAPTER XIII 



ATTENUATION OF THE VIRUS OF FOWL ENTERITIS 



The next question that I wished to answer was, 

 whether it is possible to find a means of attenuating 

 the virulence of cultures of the bacillus of fowl enter- 

 itis, in order to discover, if possible, a means of pro- 

 tective inoculation ? For this purpose two preliminary- 

 questions had to be answered : ( i ) Do the bacilli 

 form spores ? (2) Does a mild attack of the disease 

 protect the animal against a second fatal attack ? 



I. As regards the formation of spores. In all 

 experiments of attenuating the virulence of a microbe, 

 the presence or absence of spores is of first import- 

 ance. The spores being possessed of a greater power 

 of resistance would, therefore, evade the attenuating 

 influence of adverse conditions, such as certain degrees 

 of higher temperatures, chemical agencies, etc. The 

 bacilli of a culture not having the power of forming 

 spores might become attenuated in virulence, though 

 of course not killed, by degrees of temperature such as 

 55° C, and more, or by the addition of small doses of 



