VETERINARY OBSTETRICS. Ob stetrics is the art of assisting in parturition, or in the troubles incident to birth. The giving of birth to young is the culminating aet of a series of complex physiological processes, the perversion or interruption of any one of whic.h may lead to the defeat of reproduction. Some knowledge of each process is necessary in order to grasp the significance of parturition itself. Successful parturition occurs only when the prospective mother is normal in the structure and physiological development of all her organs of reproduction, and of others which may have an essential relation thereto; and the fetus must undergo a normal development before it can be born in a viable state. In veterinary obstetrics, therefore, is included all factors which necessarily precede and lead directly to rition and all immediate consequences of tiaAltut which affect the health of the mother or the yomig. The reproductive organs of the fe male consist of the ovaries, uterus or womb, vagina, vulva and the mammary glands. Of the male they are the testicles and the penis. Their specific function is the procreation of the species, including impregnation, conception, the intra-uterine nutrition and development of the fetus, its expulsion after a certain degree of development and its further nutrition for a time after birth by milk from the mammary glands until the young has acquired sufficient development to enable it to lead a wholly inde pendent existence. Before reproduction be coines possible the breeding animal must have reached the age of puberty or sexual maturity, the age at which ova and spermatozoa become mature and are discharged and sexual desire is established. Up to this age the reproductive organs are dormant in so far as their specific functions are concerned and no sexual desire is manifested.
The different species of domestic animals arrive at puberty or sexual maturity at va rious ages. The horse breeds at the age of two years, cattle at one to one and one-half years, sheep at 10 months to one year and the pig at seven to eight months of age. The rabbit breeds at six months of age.
Reproduction is a complex physiological process accompanied by or associated with phe nomena which bear an important relation tei each other. In the following order we may observe some of the processes: (1) estrum; (2) impregnation; (3) pregnancy; and (4) parturition.
Estnun or °heat° is that period of irresisti ble sexual desire which occurs in non-pregnant females at regular intervals. It is closely asso ciated with a physiological process taking place in the ovary called ovulation, in which an ovum or egg cell is shed from the ovary to traverse the oviducts and then tile uterus where, if copu lation has talcen place, the male cell (s,perma tozoan) and the female cell (ovum) unite, and the process of fertilization occurs. The es trual period and its interval in non-pregnant animals varies with the different species. In the mare the estrual period is 48 hours occur ring at intervals of four weeks during the spnng and early summer, becoming less fre quent and more irregular during autumn and may be absent during the winter. Estrum in the cow is 24 to 36 hours and occurs every three weeks with considerable regularity. In the ewe the period of heat is 24 hours and recurs in from 13 to 18 (usually 16) days. The pig remains in a state of estrutn for about three days and if not impre,gnated comes in heat again in three weeks. In carnivora estrum ordinarily occurs semi-annually in late winter and early autumn. The rabbit breeds from four to eight times a year. In all animals estrum is normally.suspended during pregnancy, but exceptions to this rule may occur.
Impregnation.—Natural • reproduction in animals can only occur as a result of copula tion which is brought about as a result of es trum of the female and the corresponding sex ual excitement of the male. During copulation the semen from the male is injected into the vagina of the female, possibly in part into the uterus. The essential condition to fertiliza tion or impregnation, so far as the male is concerned, is that physiologically perfect sperm atozoa shall gain the cervical canal, traverse the uterus and oviducts and meet the ovum. From among the myriads of spermatozoa in one discharge of semen, but one sperm •cell is essential to the fertilization of an ovum. Fertilization or conception is tht successful union of the male generative cell (sperma tozoan) with the female generative can (ovum), by wkuch the resulting cell acquires the pcnver of segmentation ana is enabled to develop into an embryo.