70 
North Carolina Experiment Station 
heavy demand made on the laboratory, although the antigenic powers of a 
vaccine prepared in this way are inferior to the living antigen because of 
the principles which might be lost through the heating process. 
The quantity of vaccine given was 1 cc. per bird during the early part of 
this work. This was due to the fact that it was deemed expedient to develop 
single vaccination if possible, because of the reluctance of the poultryman 
to submit his flock to double or triple vaccination. The number of organisms 
used was approximately 1,000,000,000 per cc. Later the dosage was increased 
to 2 cc. to the adult bird and one-half cc. to the younger ones. The field 
studies show that usually one vaccination was sufficient to immunize, only 
in three outbreaks did serious recurrence occur. 
FIG. 29.—PHOTOMICROGRAPH OF WIDAL TEST. REACTION OCCURRING 
FIVE DAYS AFTER INFECTION 
The duration of immunity produced by prophylactic vaccination against 
avian typhoid is not definitely known. This duration will probably vary 
greatly according to the reaction of the individual to the vaccine, and to the 
antigenic properties of the same. Bushnell and Patton (2) after examining 
100 vaccinated birds conclude that the duration of immunity is not over 60 
days. In the case of the single inoculation, this department carried on a 
series of adult leghorns that had received 1 cc. of avian typhoid vaccine 
for six months, attempting to infect one of these birds each month. None of 
these birds contracted the disease. Two birds which had been vaccinated 
three years prior to the artificial studies were readily infected with avian 
typhoid and succumbed to the disease. Studies of the data in the mortality 
table showing the reports on vaccination involving outbreaks during the 
past three years seems to indicate that the single inoculation has proved 
efficient in the great majority of instances. Follow-up visits to these out- 
