TESTS FOR REFRACTORINESS 755 



vented from reproducing by exposure to short days of artificial light 

 for 10 months prior to this experiment. Groups B and C had not 

 previously reproduced. Group D birds differed from group A birds 

 by a longer rest period after egg laying. Group E birds with the 

 shortest rest period were put on light treatments directly as they 

 were taken from the nest after a two-week period of intensive brood- 

 ing. For the purpose of determining whether gonadal stimulation is 

 possible after a period of production with no intervening rest period, 

 it seemed that these groups representing various intervals of rest 

 might give useful information from tissue weight responses to identical 

 stimulating treatments. 



RESULTS AND DISCUSSION 



Before treatments started, three of the groups were' checked by 

 sacrifice to establish the basic, unstimulated condition of the repro- 

 ductive tissues. Group A3 was a sample of birds maintained previously 

 for nearly a year on a short day. The values for this group may be 

 regarded as basic. In check groups Al and Dl, the values for the 

 ovary are well within those for the basic condition, while the 

 magnified values for the oviduct in these groups may be accounted 

 for by the lag in oviduct regression after periods of production not 

 experienced by group A3. For the purpose of comparison with values 

 from treated birds, whether or not we assume that a refractory group 

 had been sampled, the basic ovary to body weight ratio appears to 

 be 0.3 to 0.4 and the oviduct relationship 0.8 to 1.0 mg % (Table 

 I). 



The indices for the treated birds of all groups show significant 

 increases over the basic condition. The magnitude of increase is 3 or 

 4 times in the ovary relationship and 3 to 5 times in the oviduct 

 relationship. From a consideration of postlaying groups only, nothing 

 in their responses suggests a refractory condition. Even the incubating 

 hens, presumably under the influence of prolactin (Riddle et al., 

 1935), developed to a slightly greater extent than most of the other 

 postlaying group with long rest periods. Without the positive response 

 of group E, the responses of A2 and D2 might be interpreted as 

 being dependent upon a conditioning for stimulation by 8 or 13 weeks 



