DISEASES OP THE RESPIRATORY PASSAGES 175 



tious diseases are not agreed as to whether they are distinct 

 diseases or somewhat different types of one affection. The 

 reason for this confnsioii is readily apparent when a carefnl 

 study of the diseased l)irds is undertaken, i)rovided a suffi- 

 cient number of outl)reaks are considered. Until recently 

 they were considered as two distinct diseases; the former pre- 

 senting "scal)-like" nodules upon the skin of the unfeathered 

 portions of the head; the latter diphtheria-like false mem- 

 l)ranes in the nose, mouth, throat, eyelids and cavities iu the 

 head. Diphtheritic roup occurs in outlireaks in which the 

 skin is never affected. Contagious epithelioma may attack 

 the comb and wat- 

 tles alone, but it 

 frequently affects 

 also the lining 

 mendiranes of the 

 eyelids, the cover- 

 ing of the front of 

 the ej^eball and the 

 mouth and nostrils. 

 It is especially 

 likelv to attack the 

 borders of the eye- 

 lids and the cor- 

 ners of the mouth, 

 extending thence 

 to the surface of 

 the adjacent lining 

 membranes. "When 

 the latter are af- 

 fected, the tissue changes cannot be distinguished from those 

 which occur in outbreaks of diphtheria in which the skin is 

 never affected. 



In many infectious diseases the microorganisms which cause 

 them may be distinguished microscopically by some structural 

 or staining peculiarity; or they may be isolated and culti- 

 vated in artificial media by standard bacteriological methods 

 and recognized by some property possessed by them; in still 

 others there are certain specific reactions which may be util- 

 ized for differentiation; again the inoculation of test animals 

 may serve to identify and separate them from some other in- 

 fections. In this disease or group of diseases, those methods 

 are not available. The microorganism which causes roup is 

 not known; it caiuiot be grown artificially in cultures, nor 

 have the attempts to cultivate that which causes chickenpox 

 or contagious epithelioma succeeded. Fowls can be success- 



FiG. 66. Roup in a Chicken. 

 A, bulging of infraorbital or maxillary sinus. 



