60. Experiment Station Bulletin 345 



for sectioning. From the inoculated eggs a filterable agent was attained, 

 which when injected into susceptible chickens produced symptoms and 

 lesions similar to those of spontaneous cases but it did not produce the 

 death of the bird. 



Eight- or nine-day-old embryos appear to be the most susceptible. 

 When the virus is introduced into the artificial air cell on the side of the 

 egg, an opaque thickened area is usually observed at the point where the 

 inoculum was deposited. The center of this lesion may or may not be 

 necrotic and depressed. From the margin of the lesion there are radiating 

 opaque cordlike thickenings extending along the blood vessels of the 

 chorio-allantoic membrane. This produces a lesion that may be best 

 described as "Medusa head like". The membranes may also be markedly 

 thickened with edema. The other type of colony observed is circular 

 lesionlike as if the growth had taken place around the border of the drop 

 of inoculum. This type may also have its radiating processes and be 

 accompanied by edema of the membrane. The lesions reach their maximum 

 size after 72 hours. At 96 hours the embryos are either dead or 

 the lesions tend to localize and the edema disappears. The live embryo 

 at 72 hours shows some retardation and often hemorrhages into the skin 

 or into the peritoneal cavity. The yolk material present is thinned and 

 watery. The affected chorio-allantoic membrane carries the greatest con- 

 centration of the infectious agent, but it is also present in the embryo and 

 the embryonic fluid. 



When the infected embryonic tissues are fed or injected into sus- 

 ceptible chickens we observe a characteristic rise in the leucocyte count 

 beginning as early as 24 hours after inoculation and reaching its peak 

 at about the ninety-sixth hour, then rapidly returning to normal. This 

 leucocytosis is accompanied by a certain amount of depression, anorexia, 

 cyanosis, and edema. Diarrhea does not result, but the amount of urates 

 and mucus in the feces increases. If the birds are destroyed and nccrop- 

 sied at the time when the leucocyte count is at its height we may observe 

 the following: subcutaneous edema, generalized icterus, hemorrhages 

 into the skeletal muscles, subperiosteal hemorrhages of the flat bones, 

 subserns hemorrhage on the duodenum, petechation of heart and lungs, 

 swollen congested liver and kidneys, and acute catarrhal or hemorrhagic 

 duodenitis. iMiscroscopic lesions are similar to those observed in spon- 

 taneous outbreaks, varying only in degree of severity and extent. The 

 intestinal contents of inoculated birds are capable of reproducing these 

 lesions if fed to another susceptible bird. Any combination of or all of 

 these lesions may be observed in a single bird. All aged birds are not 

 equally susceptible. One-day-old chicks so far have been refractory to 

 intravenous, subcutaneous, and intraperitoneal injections of infective 

 material. Ten- to fourteen-wcck-old birds show the highest incidence 

 of visible symptoms following inoculation, but pullets just coming into 

 production show the most severe symptoms and lesions if affected at all. 



It has been found that the sera of birds that have recovered from the 

 inoculation will agglutinate an antigen made by suspending washed auto- 

 claved S. pnllorimi in the embryonic fluid of infected embryos. The ag- 

 glutinins appear in the blood stream about the tenth day after inocula- 



