DISEASES OF POULTRY. 221 



examination, may reveal patches of exudate in the 

 nasal passages, the mouth, the pharynx or larynx. 

 In some cases no local manifestations can be detected 

 and diphtheria is only suspected because other mem- 

 bers of the flock with similar symptoms present the 

 false membranes. 



The course of the disease varies from a few days in 

 the acute form to several weeks in the chronic form. 

 In the very acute cases the disease is exceedingly 

 destructive and a large part of the flock may die in a 

 few days. The chronic form may not cause many 

 deaths, but renders the birds unproductive for weeks 

 or months. Between these two extremes there are all 

 gradations of virulence. 



The period between exposure to the contagion and 

 the development of the symptoms may be only three 

 or four days or as long as two weeks. The disease 

 produced by inoculation appears within ten days with 

 fowls and within three days with pigeons. 



Causation. — The diphtheria of birds is undoubt- 

 edly contagious. It is usually introduced into a flock 

 by the exposure of the birds to sick ones at shows or 

 by bringing affected birds on the premises. The 

 contagion may be carried by birds which have the dis - 

 ease in so mild a form that they show no symptoms of 

 it. There is a general belief that the disease may be 

 developed by exposure of birds to draughts of air, or 

 by keeping them in damp, filthy and badly -ventilated 

 houses. This opinion is probably incorrect and is. 

 accounted for by the early symptoms of acute diph - 

 theria, and those of all stages of the chronic form, re- 

 sembling the symptoms seen in catarrhs and colds. 

 Dampness and lack of ventilation no doubt favor the 

 maintenance and development of the contagion and 



