AVIAN DIPHTHERIA AND BIRD POX 107 
and degree according to the severity of the infection. Thus, chronic 
mild infection of the mucous membrane does not always produce ab- 
solute immunity. Infection of the mucous membranes alone will 
induce an absolute immunity against inoculation of the skin. Vari- 
ous authors have demonstrated immunity in fowls for periods vary- 
ing from 2 months to 2 years. Live virus only has been shown to 
confer immunity and the injection of killed virus has no immunizing 
effect. 
A number of workers have attempted the immunization of fowls 
against diphtheria and chicken pox and treatment of the same 
conditions by means of a vaccine prepared from the exudates and 
pox nodules of affected fowls. The material is ground up in a suf- 
ficient amount of normal salt solution to form a suspension and is 
filtered through cotton to remove large particles. It is then diluted 
until it appears moderately cloudy and heated at 55° C. for 1 hour. 
Doses of 1 ¢.c. are injected subcutaneously on two or three occasions 
with intervals of 5 to 7 days. 
A product prepared by this method has been favorably reported 
upon as an immunizing and curative agent by several workers. Ex- 
periments by the present writers have not sustained the claims made 
for the immunizing value of a vaccine prepared by this method. 
Fowls which have been vaccinated and later artificially inoculated 
with virulent material have developed characteristic internal and ex- 
ternal lesions of diphtheria with accompanying fatalities. 
Bacteriology of avian diphtheria. Many investigations of the 
bacteriology of avian diphtheria were made previous to the recogni- 
tion of the role of pox virus in causing diphtheritic lesions, so it 
is not possible to determine whether the lesions were primarily due 
to pox virus, or were due to bacteria alone. Other reports of in- 
vestigations conducted more recently do not contain evidence that 
pox virus was not concerned in the causation of the lesions. 
Extensive investigations of the bacteriology of avian diphtheria 
have been made by Harrison and Streit, Bordet and Fally and by 
Hausser. 
Moore first reported finding a member of the hemorrhagic septi- 
cemia group in diphtheritic lesions in fowls, which observation has 
been confirmed by a large number of investigators. Sigwart has 
observed the spontaneous appearance of fowl cholera in birds af- 
fected with diphtheritic lesions of the mucous membranes. In these 
cases the primary cause of the diphtheritic lesions was considered 
to be pox virus. He explains the occurrence by assuming that the 
