6 MASS. EXPERIMENT STATION BULLETIN 337 



Experiments Without Red Mites 



When the preceding experiment was completed, the house was carefully- 

 disinfected with 5 percent cresol solution and dried before any birds were placed 

 in it. On October 24, 1935, the second experiment was started and continued 

 to July 1, 1936. Data are given in Table 4. 



Table 4. — Chickens Exposed to Natural Infection with 

 Myeloleukosis in a House Free of Red Mites 



Pullets MH-42974, MH-42975, MH-42976 and MH-42977, previously in- 

 oculated with myeloleukosis, died on the 5th, 6th, 10th and 17th days, respec- 

 tively. 



Pullets MH-42980, MH-42978, MH-42971 came down with myeloleukosis 

 in 25, 30 and 47 days after the experiment commenced, and died 41, 35 and 29 

 days later. One pullet, MH-42979, became an internal layer and died of 

 peritonitis. The remaining 15 pullets and 2 cockerels lived 247 days, which 

 was the duration of the experiment. This investigation may have been in- 

 fluenced by the weather, since it was not started until October 10. However, 

 the weather was warm up into December, and this mild period corresponds 

 with the duration of the myeloleukosis, since the last bird to come down with 

 the disease did so on December 10, 1935. 



It is interesting to note that myeloleukosis died out in both flocks soon after 

 freezing occurred. In Flock 1, infested with red mites, seven birds contracted 

 myeloleukosis, one recovered, and six died. In Flock 2, free of mites, three died 

 of myeloleukosis. These experiments indicate that red mites are a vector in 

 myeloleukosis, since twice as many birds died in Flock 1 as in Flock 2; but 

 this is not the only way in which the disease is spread, or there would have been 

 no deaths from this cause in Flock 2. That so many of the birds, 61.9 percent 

 in Flock 1, and 71.42 percent in Flock 2, appeared to be resistant was a sur- 

 prise; and that the number of days that the birds were myeloleukotic varied 

 from 7 to 120, the average for 10 birds contracting the disease naturally in both 

 experiments being 35.3 days, was unexpected. The eight control birds on both 

 experiments averaged to live 9.25 days only. These chickens when inoculated 

 probably received larger doses of the virus than the chickens affected naturally. 



