9 



chronically affected ; and then the first cold nights give the disease a 

 fresh start. 



Young fowls and fowls of the tine breeds are especially liable to 

 roup. While some poultry men maintain that birds once having 

 suffered from roup never take the disease again, most of the experi- 

 mental evidence tends to show that no acquired immunity exists, as 

 sometimes happens after other diseases. Some fowls are, however, 

 naturally immune, and never take the disease. In the course of our 

 own experiments, a white chicken which had never had roup, was in- 

 oculated with repeated and large doses of the roup germ, but without 

 effect. 



V'lg a. — Head of fowl 36; twenty-two days after inoculation 

 with a culture of the roup bacillus— n, false membrane. 



The Cause of the Disease. 



Many opinions have been expressed as to the cause of the disease ; 

 and some of these have been based on scientific research, while others 

 have been mere guesses. Some writers have thought that the disease 

 is due to " Protozoa," alow form of animal life ; and others have isola- 

 ted various bacteria from the disease tissues, which bacteria when 

 grown in pure culture and introduced into healthy hens, have pro- 

 duced symptoms of the disease. 



As roup, especially when located in the mouth or throat, resembles 

 human diphtheria, it has been claimed that the well-known organism 

 of this disease, the Bacillus dijjhtheriae of Klebs-Loeftler, is the cause 

 of roup, or, as it is termed by some, " fowl diphtheria." 



