AVIAN DIPHTHERIA AND BIRD POX 97 
tion and furnishes a basis for clearing up the confusion. Among 
writers who have studied both avian diphtheria and pox and who 
agree on this point are Uhlenhuth and Manteufel, Schmid, Bertegh, 
and Sigwart. 
Whether there are other specific infectious diseases of fowls char- 
acterized by diphtheritic lesions not due to pox virus, remains to be 
determined by further investigation. The idea has been advanced 
that diphtheritic lesions of the mucosa of the head of the fowl may 
result from invasion by various bacteria. 
There is ground for questioning the validity of differentiating 
into separate disease entities such conditions as simple catarrh, com- 
mon colds, contagious catarrh, influenza and coryza. In large in- 
fected flocks, birds with catarrhal lesions alone, diphtheritic lesions 
alone, and pox lesions alone will be found in close association with 
others perhaps exhibiting all these lesions. Clinical evidence in 
such flocks points very strongly to the conclusion that the cases 
characterized by the presence of serous exudate in the nostrils are 
but the early stages of avian diphtheria. Insufficient etiological ev- 
idence is available to justify recognizing such conditions as specific 
infectious diseases. 
Characterization. Avian diphtheria is an infectious disease, 
manifested by the formation of catarrhal exudate in the nasal cavity, 
eyes, and sinuses associated with pseudo-membranes in the mouth 
and wart-like nodules on the external surface of the head. Until 
recent years, the term diphtheria or roup was applied to cases 
showing the internal exudative lesions, while those with external 
growths were designated bird pox, chicken pox or epithelioma con- 
tagiosum. The discovery that a single causative agent can produce 
both types has resulted in the two conditions being classed as simply 
external and internal lesions of one disease. 
Etiology. Diphtheria and bird pox are caused by a virus the 
nature of which is not well known. The organism has not been cer- 
tainly identified micrcscopically and is so small that it will pass 
through a Berkefeld filter. However, according to Marx and 
Sticker, it will not pass through a porcelain filter. 
Widely diverging opinions concerning the nature of the virus 
have been expressed by the various writers who have studied the dis- 
ease. Friedberger and Frohner assigned protozoa of the class gre- 
garina as the cause. Borrel described certain cell inclusions for 
which Lipschiitz has suggested the name Strongyloplasma avium. 
Halasi believes the etiological agent to be a chlamydozoon. 
