No abstract

No abstract

The time of onset of permanent insensibility, subsequent to incision of the major blood vessels of the neck, was studied in eight one-week-old calves. Insensibility was determined from the study of electroencephalograms (EEG). Apart from one animal in which insensibility first occurred within 34 s, the first indication of insensibility did not occur until between 65 and 85 s. All animals subsequently showed evidence of periodic resurgence of possible sensibility for up to 123 to 323s after slaughter. Such resurgences were seen to be preceded by a respiratory gasp. The EEG did not become isoelectric until between 132 and 336 s. Involuntary movements of the animal and the presence of corneal and palpebral reflexes persisted for up to 300 s after slaughter. It is suggested that the marked increase in the time for insensibility to occur after slaughter in calves, compared with sheep and lambs, is due to a greater contribution of blood to the brain by the vertebral arteries in calves.

SUMMARY1. The normal passage to the abomasum of liquid sucked by lambs and calves was confirmed in radiographic studies to be changed to passage of liquid to the reticulum and rumen after cervical or abdominal vagotomy.2. The effects of hexamethonium (8-10 mg kg-1 i.v.) were similar to those of vagotomy.3. Atropine (200-800,g kg-' i.v.) had either no detectable effect on the destination in the stomach of liquid sucked by lambs or caused a partial failure of the reticular groove mechanism.4. Fluid sucked by lambs passed wholly to the abomasum after adrenaline (5-40 #ug kg-' i.v.).5. Atropine and adrenaline caused a greater dysfunction of the reticular groove mechanisms in calves than in lambs.6. Contraction of the reticular groove was observed via rumen fistulae in three lambs. Eversion of the caudal oesophagus into the reticulum which occurred when saliva was swallowed into the reticulum and rumen was not observed when liquids were sucked from a bottle.7. The continued passage to the abomasum of sucked liquid in atropinized lambs has been taken as an indication of the importance of caudal oesophageal reactions, tonic activity of the reticular groove and the atropine-resistant vagally induced opening of the reticulo-omasal orifice in the reticular groove mechanism.

5. Opening of the orifice and disappearance of spontaneous closing movements followed more intense stimulation of the vagus nerves.6. Vagal opening effects were obtained after atropine was given and after adrenergic opening and closure effects had been blocked with phentolamine and propranolol.