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Five acyclic spring-calving beef cows (20-40 days post partum) were bled every 15 min for 60 h and thereafter every 6 h for 5 days. Gn-RH (5 micrograms) was injected every 2 h for 48 h, starting 12 h after sampling began. Pulsatile patterns of LH release occurred synchronously in response to injection and 4 of the 5 treated animals subsequently ovulated and completed at least one full ovarian cycle. Four of 6 similar control cows were bled every 10 min for 8-h periods at equivalent times post partum. Pulses of LH were seen after approximately Day 25 post partum with a mean pulse frequency of 0.5 per h. There was little evidence of a discrete pulsatile mode of FSH release in any of the treated or control cows. The time to the first significant progesterone rise in the 4 treated and ovulating cows (34.5 +/- 5.6 days post partum) was significantly shorter (P less than 0.05) than in the 6 control animals (66.3 +/- 11.4 days).

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betkveen the two samples. It may be anticipated, furthermore, that asphyxia or hyperventilation (as forced breathing) will lead to significant fluctuations in tlie prothrombin activity of the blood.Loss of UO, niay also account in part for tlie diniiiiutioii in prothrombin activity of plasnia after being heated to 56°C for 15 minutes, or after staiidiiig at .5' 0 for several days.Exposure of citrated or oxalated plasnia to an air current is followed by a rapid diniiiiution in its prothi-onibin activity ;this is corrected bqthe addition o i CO, a i d not affected by oxygen.Siitiiiitnry. 13532Hormone-Induced Ovulation in Domestic Fowl.Multiple ovulatioiis in hens have k e n effected iii tlie laboratories of tlie Bureau of Animal Industry Iiy intravenous adiiiiiiistration of a luteinizing preparation after pretreatment with pregnant mare's serum. So far as the authors are aware, this is the first demonstratioii of direct experimentally induced ovulation in birds.Owlation has been iiiduced in a iiuiiiber of nianinialian species by administration of anterior pituitary hormones or anterior pituitarylike Kirschbauni, ct (11. ,' and lVitschi3 have described full ovarian function in small caged passerine birds following prolonged stimulation with pregnant mare's serum. Increase in rate of ovulation is implied in the results of Clarkj4 Gutowska6 and Dubowik,' but Bates, Lahr and Riddle' clearly denioiistrated that doses of follicle-st imulating hornione or pregnant niare's serum sufficient to cause marked follicular growth in the laying lien and pigeoii also caused cessation of ovulation, usually by the fourth day. These results of Bates, 4t d. ,' have been confirmed repeatedly in this labora-1 Hartman, Carl G., Chapter TX, pp.

Progesterone concentration was measured in milk samples collected twice or three times weekly from 157 suckling beef cows in three herds during the period from parturition until the resumption of ovarian cycles. The length of the post partum acyclic period varied between cows from 11 to 125 days. The length of the acyclic period did not differ between cows suckling one or two calves or between the two breeds of cow studied. There were significant negative correlations between the length of the acyclic period and 1. body weight at calving (r = -0-394; P<0-001) and 2. days from calving to the next longest day of the year (r=-0-782; P<0-001). Cows calving between February and April were acyclic significantly longer (83 days) than those calving between August and December (44 days; s.e. of difference = 3-5; P < 0-001). In one herd there was a significant negative correlation between the length of the acyclic period and order of calving both in spring (r=-0-379; P<0-05)-and autumn/winter (r=-0-349; P < 0-05)-calving cows. Of the 40 spring-calving cows in the same herd, 17 were served naturally prior to any rise in milk progesterone concentrations and 11 of these conceived to this service.