Diseases of the Respiratory System 165 



separate diseases although in early stages they cannot be 

 distinguished. There has also been a considerable discussion 

 of the possible identity of avian and human diphtheria, but 

 the evidence that these are distinct seems conclusive. Diph- 

 theritic roup is distinguished from nasal roup by the forma- 

 tion of false membranes on the mucous surface of the nostrils, 

 eyes, mouth, throat, trachea or bronchi. These membranes 

 are a tough, grayish or yellowish growth and adhere very 

 firmly to the underlying tissue. 



The first symptoms appear in from three to five days after 

 exposure to contagion. The duration of the disease varies 

 from a few days to several months. Many birds in the 

 flock appear to be naturally immune or sufficiently vigorous 

 to overcome the disease without the formation of the charac- 

 teristic lesions. On account of mild, undetectable cases 

 diphtheritic roup is very hard to eradicate without sacrificing 

 the whole flock, disinfecting the premises, and starting anew 

 with incubator chicks or clean purchased stock. 



Diagnosis. — Following the excellent account given by 

 Salmon it may be said that diphtheria begins as a local ir- 

 ritation or inflammation at some point on the internal sur- 

 face of the mouth, throat, nostril or eyes. At this time the 

 general health is not yet afi"ected, and there is nothing but 

 the diphtheritic deposit to indicate that the bird has been 

 attacked. This deposit is at first thin, yellowish or whitish 

 in color, and gradually becomes thicker, firmer, and more 

 adherent, so that considerable force is required to remove it. 

 The mucous membrane beneath the deposit is found, when 

 the latter is removed, to be inflamed, ulcerated, and bleed- 

 ing, but it is soon covered by a new deposit. This deposit 

 is called a false membrane, and when it is situated where the 

 air passes over it in breathing it dries, becomes uneven and 

 fissured, and its color changes to a dark brown. 



While the false membranes over the parts first affected are 



