Formulas that approximate the composition of human milk are widely used as the sole source of nutrients for infants during the first months of life. Such formulas contain milk, soy, or meal proteins, or protein hydrolysates together with those forms of fat carbohydrate, vitamins, and minerals shown to be bioavailable to the infant. Legislation concerning nutrient composition and quality assurance of products labeled as infant formulas has been enacted by Congress. Governmental and industrial standards also help to assure microbiological safety and stability. Problems of nutrient composition and adverse reactions have occurred during the evolution and development of infant formulas. Problems concerning nutrient deficiency are now almost unknown, but adverse reactions of individuals to specific formula ingredients continue. Accurate information on composition and related nutritional properties of infant formulas is essential for their effective use and for the avoidance of undesirable complications.
It was shown previously by Chinn and Wang that dogs exposed to 800 r total body irradiation vomited within 2 hours after completion of exposure. After chronic destruction of the chemoceptive emetic trigger zone, no dogs vomited within 2 hours of radiation. It was observed that these operated animals would vomit later throughout their period of survival. Visceral deafferentation alone (abdominal vagotomy and sympathectomy) did not prevent dogs from vomiting soon after irradiation or within several days. On the other hand, both acute and delayed emesis due to irradiation was not observed in dogs with chronic destruction of the chemoceptive trigger zone and abdominal visceral deafferentation. It appeared, therefore, that delayed vomiting following lethal total body irradiation was mediated through two mechanisms; the centrally located trigger zone, and the peripheral visceral afferent receptors of the vagus and sympathetic trunks.
Motion sickness was experimentally induced in dogs by means of a standardized swinging exposure. Susceptible dogs were selected for surgical extirpation of the labyrinths or various parts of the cerebellum. It was found that animals showed no vomiting responses to long exposures of swinging motion after bilateral labyrinthectomy or ablation of the nodulus and uvula. Even with incomplete extirpation of these structures, animals would become partially or totally resistant to motion sickness. In general, these operated animals exhibited normal responses to intravenously administered apomorphine or orally administered copper sulfate. These results indicate that motion stimulates the labyrinthine receptors, and the vestibular impulses traverse the nodulus and uvula of the cerebellum, and the chemoceptive emetic trigger zone, and finally reach the medullary vomiting center.
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