XIII ATTENUATION OF VIRUS OF FOWL ENTERITIS 115 



(4) In this series the broth culture was heated to 

 55° C. for 20 minutes and then inoculated in the same 

 quantity as before into eight fowls. They were all quiet 

 and off their food on the 6th and 7th days, but there 

 was no diarrhoea ; on the loth day they seemed to all 

 appearances right again. This was then the result 

 aimed at, and it now only remained to be proved that 

 these same fowls were capable of withstanding a 

 second inoculation with virulent material. For this 

 purpose a broth culture, 24-48 hours incubated at 

 '^']'' C, was used for inoculation, two control fowls 

 being at the same time inoculated with the same 

 broth ; each of these ten fowls (that is the eight that 

 had been subjects of the first inoculation and the two 

 control fowls) received one whole Pravaz syringeful, 

 i.e. a considerable dose. The two control fowls be- 

 came ill and were dead on the 7th day from the typical 

 fowl enteritis, the eight other fowls remained perfectly 

 well. From this, I think it follows that a recent broth 

 culture heated to 55° C. for 20 minutes can be taken 

 to represent a fluid suited for protective inoculation. 

 Such a broth culture when tested by sub-culture 

 yields good and virulent growths, so that while the 

 heating to 55° C. for 20 minutes impairs the virulence, 

 it does not impair the vitality of the bacilli. 



(5) A series of experiments which deserves mention 

 was instituted to see, whether under natural conditions 



