ing the infection from the premises through testing or replacements from clean 

 stock or by a combination of both methods. 



Mention should be made also of the improvement in increasing the number 

 of 100 percent tested flocks as compared with the previous season. Flock owners 

 are reminded again of the importance of testing all birds on the premises in order 

 to determine the true status of the plant. Furthermore, the Massachusetts 

 Department of Agriculture does not consider partially tested flocks for the 

 official pullorum tested grades established by that Department. 



Table 3. Range of Infection in the Positive Flocks 



Appearance of Infection in Flocks Previously Negative 



During the past year, infection was detected in ten flocks which were negative 

 the previous season. In the majority of cases, no definite source of infection was 

 determined. The data in Table 4 show that only three of the flocks (3, 4, 10) 

 had been negative for more than one year. 



The owners of flocks 3 and 4 could not account for any definite source of in- 

 fection. Flock 3 was tested on January 16, 1939, and revealed only one reactor 

 (pullet) from which 5. pullorum was isolated. The owner reported that new 

 stock had been introduced in the form of hatching eggs and baby chicks the 

 previous spring, but the sources from which the stock was selected were regarded 

 as free from pullorum infection. Flock 4 was tested on December 15, 1938, and 

 revealed two strong reactors and two doubtful reacting birds. The two strong 

 reactors (pullets) were necropsied and yielded S. pullorum. The owner was able 

 to present evidence that might be only remotely responsible for the infection. 

 On retest, both flocks were negative. These two flocks represent typical cases of 

 "breaks" which occur very infrequently. Such cases should point out that the 

 infection is not always introduced through custom hatching, purchase of infected 

 stock, and contest birds, but possibly may come indirectly from used feed bags, 

 egg crates, etc. The fact that so few birds were infected would strongly suggest 

 such an avenue of infection. 



The results in Table 4 emphasize to the buyer of pullorum-clean stock that a 

 flock which has passed a negative test for several consecutive years is a safer 



