SummarySingle blastomeres of four-and six-celled pig eggs, either enclosed in their own zona pellucida, or injected into a foreign zona pellucida, were transferred to recipient gilts which were autopsied 5-6 days later. A control group in which the zona pellucida was penetrated without disturbing the blastomeres was included in the experiment.At autopsy the following percentages of transferred eggs were recovered as normal blastocysts: zona penetrated, 77% (22 eggs transferred); single blastomeres in own zona, 35 % (48 eggs transferred); single blastomeres in foreign zona, 0 % (30 eggs transferred).The possible reasons for partial failure of single blastomeres to develop in their own zona pellucida and complete failure of those in a foreign zona pellucida are briefly discussed.
When semen is ejaculated, its different components are not discharged all at once, but follow one another in a definite order of sequence. It has been possible to demonstrate this clearly in man, through the application of the so-called 'split-ejaculation' method. In man, the ejaculation is initiated by the secretion of Cowper's gland; the prostatic secretion comes next, to be followed by the sperm and the vesicular secretion (Huggins & Johnson, 1933;MacLeod & Hotchkiss, 1942). According to more recent data provided by Lundquist (1949), less than 10 % of the human ejaculate is contributed by the sperm and epididymal secretion, 12-8-32-5 % by the prostatic secretion, and 46-3-80-4 % by the vesicular secretion.In experiments on animals the technique of fractionate collection has been successful in species in which the ejaculation is physiologically a slow process. An animal well suited to this type of experimental approach is the boar, with an ejaculation period lasting up to 30 min. According to McKenzie, Miller & Bauguess (1938), less than 5 % of the boar e j aculate is made up by the sperm and the epididymal secretion, whereas the urethral glands contribute up to 70 %, Cowper's glands 10-25 %, and the seminal vesicles 15-20 %, of the total ejaculate. Somewhat similar conditions prevail in the stallion (Lambert & McKenzie, 1940; Day, 1940).In the bull, however, unlike in the boar and stallion, the ejaculation is rapid and is completed within a few seconds. Therefore, it is not practicable to collect separate fractions of bull semen ejaculate by means of the artificial vagina. As an alternative method, several investigators have applied to bulls the massage method of collection (cf. Anderson, 1945). However.for the purpose of distinct fractionation, specimens obtained in this manner were seldom of practical value.In the present investigation, use has been made of the electro-ejaculation method, developed by Thibault, Laplaud & Ortavant (1948). By applying electrical stimulation, we have been able to collect and examine two main well-defined fractions of bull semen, an early one during the initial phase of stimulation, very copious and completely spermfree, and following upon it, a later one, containing the sperm. We have devoted our attention to a study of the chemical composition of the pre-sperm Journ. Agric. Sci. 43 fraction; furthermore, the findings made with this secretion were compared with results obtained on the sperm-containing fraction, as well as with bull semen specimens collected in the ordinary way, without electrical stimulation, and occasionally also with the seminal vesicle secretion collected from the glands of freshly killed bulls. EXPERIMENTALThe collection of bull semen fractions by electrical stimulation was carried out according to the technique described in detail by Thibault et al. (1948), with the aid of a rectal electrode, which was kindly made available to one of us (L.E.A.R.) by Dr Thibault. The ejaculate was collected into several separate glass tubes; the samples which were found ...
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