The development of the central nervous system of the sheep foetus with particular reference to myelin forming cells and myelination has been studied by morphological and histochemical methods. The development of the spinal cord resembles that described for other species and broadly similar patterns of development have been found for the other major regions. Differentiation of definitive cell types is marked by the appearance of cytochrome oxidase activity in their cytoplasm. In gray matter strong cytochrome oxidase activity persists into post-natal life whereas in white matter activity declines following commencement of myelination.Lipids having the histochemical reactions of myelin first appear in a particular region as the capillary circulation of that region develops. It is suggested that phospholipid elements of perivascular lipid may be rapidly incorporated into the developing myelin sheath whilst galactolipids from the same location are more slowly utilized. The implications of the findings are discussed.

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Analysis of field data suggested that listerial encephalitis in sheep was most common in winter and early spring in the age groups of sheep which would be cutting, changing and possibly losing teeth. It was hypothesised that under these conditions ingested Listeria monocytogenes could reach the fine dental terminals of the trigeminal nerve causing an ascending neuritis and encephalitis. Experimental inoculation of organisms into the dental pulp demonstrated the feasibility of this route of infection. Histological encephalitis was evident six days after inoculation but the incubation period to clinical neurological disease was at least three weeks.

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The birth and fate of 818 lambs born to 571 ewes on a low-ground farm in the Scottish Borders with a history of substantial perinatal mortality were monitored with a range of physiological, biochemical and pathological measurements. In lambs which survived, the rectal temperature, birthweight and plasma concentrations of fructose, insulin, thyroxine and the third component of complement at birth, and the weight at four months of age, decreased with litter size. One hundred and thirty-seven lambs were stillborn or died within four days and seven others died later. The mothers of 77 per cent of these lambs had low condition scores, but the lamb deaths did not correlate significantly with the condition scores. From data relating to birthweight, temperature, packed cell volume and plasma composition it was deduced that placental insufficiency was involved in 24 per cent of these deaths; acute hypoxaemia at birth accounted for 35 per cent, inadequate thermogenesis for 12 per cent and starvation for 13 per cent. The remaining 16 per cent of dead lambs could not be assigned to any of these categories. Using only clinicopathological criteria, 37 per cent of the lamb deaths were attributed to antenatal influences which included immaturity, developmental anomalies, and degenerative or inflammatory changes. Thirty-three per cent of the deaths were due to post natal factors which included, in declining order of frequency, starvation, enteritis, misadventure, pneumonia, navel infections and septicaemia. No conclusions could be drawn from the pathological examinations alone in the remaining 30 per cent, although almost half of these had low rectal temperatures after birth, death being attributed to hypothermia.(ABSTRACT TRUNCATED AT 250 WORDS)