Fertilized eggs were transferred into the uterine horns of recipient rats which had been ovariectomized 4 days before and had recieved daily injections of 4 mg of progesterone thereafter. Eggs transferred were obtained from normal pregnant rats by flushing the oviducts or the uterine horns with physiological saline. Ovular ages at transfer were from Day 1 (day when spermatozoa were found in vaginal smear) to Day 5 (blastocyst). From 4th day after the transfer, one μg of estrone was injected daily together with progesterone. Recipient rats were killed 8 to 9 days or 14 to 22 days after the transfer and were examined for implantation sites and living fetuses.
The proportion of the number of implantation sites to the number of eggs transferred were 2/37 (5.2%), 24/110 (21.8%), 13/66 (19.6%), 20/65 (30.7%) or 50/152 (32.8%) for 1, 3, 3, 4 and 5 days old eggs, respectively. Three fetuses were found in a recipient rat which had been transferred eight 2 days old eggs (2-cell stage). Nine fetuses were also found in four recipient rats transferred blastocysts.

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For the assay of relaxin, response to the hormone of the pubis symphysis of guinea pig is usually used. It seems that the repeated use of the guinea pig for the test reduce the sensitivity of the animal to relaxin and this is one of causes of variation in the assay.
Intact female guinea pigs weighning initially 350 to 450 g were injected 15μg of diethylstilbestrol every week throughout the present study. Daily injection of 2 GPU of relaxin for 8 days reduced the response of the symphysis pubis gradually and at 8 days to the extent of one sixth to one tenth of initial response.
Thereafter, 2 GPU of relaxin was injected every week to each animal of the group. Sensitivity of the symphysis pubis of the group did not recover the initial level and completely negative at the fifth week. After 10 days following the series of injection of relaxin, 1.5 mg of progesterone was injected daily for a period of 8 days. The injection of progesterone caused the symphysial relaxation in all animals of the control group, but not at all in the relaxin injected group.
These results show that repeated injection of relaxin even if during a comparatively short period induced an acquisition of resistance to relaxin.

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The immunological assay with anti-PMSG surum has been used for pregnancy diagnosis on 332 sera obtained from mare 40-104 days after copulation.
The results were compared with those obtain by the Aschheim-Zondek test. Two hundred and sixty nine of the sera were gave a positive and 63 a negative reaction. Five false positive reaction in 269 positive cases and 16 false negative reaction in63 negative cases were found. Two false positive reaction were also found in 91 control mare sera. Sixty five cases from gelding sera were all negative.
The first positive pregnancy reaction occurred at 42nd day after copulation and last positive pregnancy reaction at 96th day. The suitability of the method applied as a pregnancy diagnosis on 332 cases was 93.7% and 95% confidence intervals of its suitability was 95.48-90.90%. The time of pregnancy diagnosis with immunological assay might be considered at the 9th week of pregnancy.

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