APPEARANCE OF INFECTION IN FLOCKS PREVIOUSLY NEGATIVE 



In Table 3 are listed nine flocks which were negative in 1933-34, and revealed 

 infection in 1934-35. The source of the infection was accounted for in four flocks 

 as originating from custom-hatching or purchase of questionable stock. In five 

 flocks the origin of infection remained obscure. In the majority of "breaks" the 

 flocks possessed only a short non-reacting testing history (one or two years). 

 In three flocks the infection was completely eliminated through intensive re- 

 testing. While the number of "breaks" is small, it reveals that non-reacting 

 flocks can become re-infected; hence the need for annual testing becomes apparent. 

 Also the importance of efi^ective preventive measures should not be ignored by the 

 flock owner. The re-introduction of infection has involved additional expense 

 through retesting, as well as from other points of view. The flock owner should 

 be continually on his guard against infection which may enter through various 

 channels. In this manner it will be possible to reduce the number of "breaks" 

 to a minimum. 



Table 3. -Appearance of Infection in Flocks Previously Negative 



♦Represents retests. 



