12 MASS. EXPERIMENT STATION BULLETIN 311 



anyway, because for a number of years the flock from which the roosters were 

 purchased had had an outbreak of infectious laryngotracheitis every fall, which 

 lasted nearly all winter, and the disease was first introduced into this flock by the 

 purchase of breeding cockerels, before vaccination against this disease was 

 known. 



It is evident that adult birds from vaccinated flocks and from flocks having 

 natural outbreaks of infectious laryngotracheitis should not be placed in flocks 

 free of this disease, because of the danger of carriers. Unfortunately no satis- 

 factory way of detecting chronic carriers of infectious laryngotracheitis is known 

 at present. 



Flock 6 



The owner of this flock had attempted the eradication and control plan, but 

 apparently the premises were not properly disinfected and the disease broke out 

 almost simultaneously in two different pens after about two-thirds of the pullets 

 had been moved in from the range. No vaccine was available to treat the flock, 

 so it was decided to attempt to stop the disease by making up the vaccine on the 

 farm from the virus occurring naturally in the outbreak. 



It took four men three days to vaccinate this flock of 3,600 birds at the rate 

 of 1,200 per day, working eight hours a day. 



Other observations, besides those recorded in Table 6, were made on the 

 vaccinated birds, as follows: 



(1) 3,100 or 86.11 percent showed takes and no symptoms of disease. 



(2) 330 or 9.16 percent showed both takes and symptoms of infectious laryn- 

 gotracheitis, and 10 or 3.03 percent of them died. 



(3) 134 or 3.74 percent showed no takes and no symptoms of disease. 



(4) 36 or 1.00 percent showed no takes and symptoms of disease, and 20 or 

 55.55 percent died. 



Flock 7 



August 7, 1933, the writer visited a poultry farm on which an outbreak of 

 infectious laryngotracheitis had just begun. This poultryman had started in 

 the business the year before by purchasing pullets and cockerels from breeders 

 and bringing them together in a single house. Infectious laryngotracheitis broke 

 out soon after the birds were housed and lasted all winter, so that the owner 

 decided to slaughter the birds for local trade. 



A new house was built about 10 feet from the one in which some of the old 

 birds still remaining on the farm were kept, and the first lot of pullets which 

 had begun to lay had been placed in it 10 days before developing an outbreak 

 of infectious laryngotracheitis. In the meantime, the disease appeared in some 

 of the chickens on the range, which was about 20 feet from the new poultry house. 

 There were approximately 800 chickens on the range. 



It was decided to vaccinate the chickens using vaccine prepared from the 

 pullets which had contracted the disease first and were hopelessly lost, since all 

 of them were sick, a few had died, and about half of those remaining probably 

 would die in the next three or four days. Unfortunately the writer did not have 

 his vaccination outfit with him as the trip was taken for an entirely different 

 purpose, and it was necessary to use improvised equipment. The applicators 

 were split from kindling in the wood pile, cotton for making swabs was secured 

 from the family medicine closet, scissors from the sewing room, a bowl and a 



