DIPHTHERIA IN FOWLS 485 
Ps. pyocyaneus has been obtained in pure culture from the exudates, 
Mack failed to produce the disease with B. cacosmus. 
Guérin considers it a general disease caused by a coccobacillus 
which is not unlike the bacterium of septicemia hemorrhagica. He 
finds it in the blood and organs. Those who believe that chicken pox 
is identical with roup believe the cause to be a filterable virus. It has 
been suggested that the filterable virus is not very virulent but that 
the secondary bacterial invaders are largely the cause of the lesions. 
Roup is usually introduced into a flock by the exposure of the birds 
to sick ones at shows or by bringing affected fowls on the premises. 
Fic. 110. FOWL SHOWING EYE CLOSED. THE CONJUNCTIVA IS COVERED WITH A THICK 
EXUDATE (Ward). 
The contagion may be carried by birds which have the disease 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 to draughts or by 
keeping fow]s in damp, filthy and badly-ventilated houses. There 
seems to be confusion concerning the early symptoms of acute diph- 
theria and those of all stages of the chronic form, with those of simple 
colds and catarrhs. Ward was unable to produce the disease by 
exposing fowls to unfavorable conditions, but when infected fowls were 
