The ceca of newly hatched chicks obtained either from commercial hatcheries or from a carefully controlled experimental hatchery have been shown to contain high numbers of a variety of microorganisms. Fecal streptococci, clostridia, enterobacteria, pediococci, and occasionally Pseudomonas aeruginosa have all been isolated, but never lactobacilli. After the chick has been on feed for 1 day, the numbers of lactobacilli in the crops and ceca are quite variable; by the 3rd day, however, large numbers are present throughout the alimentary tract. Lactobacilli could be established after 1 day by incorporating them in the feed or by treating the chicks with 0.5 ml of a broth culture. Spraying the eggs before hatching did not lead to their early establishment. Lactobacilli given alone to the newly hatched chick failed to prevent the establishment of Salmonella. However, when the chicks were given a complex mixture of facultative anaerobes and anaerobes which had been isolated from an adult bird, cecal colonization with Salmonella was prevented. The possible importance of the facultative anaerobes, particularly Streptococcus faecalis, in lowering the redox potential to encourage the growth of the anaerobes is discussed.

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A method of 'rearing and maintaining chickens from day old to 80 weeks of age free from infectious bronchitis, Newcastle disease, infectious avian encephalomyelitis, CELO and GAL viruses, lymphoid leukosis, Marek's disease, Mycoplasma gallisepticum, Salmonella pullorum and other Salmonella spp., Staphylococcus aureus, Eimeria spp. and helminths is described. The advantages of glass fibre isolators each with its own ventilation system are outlined.

Paralysis due to peripheral neuritis occurred sporadically in a flock of Rhode Island Red chickens over a period of 8 years and is named idiopathic neuritis (IP). The flock was housed in isolators and free from many common pathogens including all known neurotropic viruses of chickens. The pathology of the nerve lesions, including their ultrastructure, is described and comparisons made with the lesions of Marek's disease and experimental allergic neuritis in chickens. Demyelination with invasion of nerve fibres with lymphocytes and macrophages occurs in all three diseases but there are differences in lesion distribution and intensity of cellular infiltration. The closest similarity is between the lesions of IP and the B-type lesions of Marek's disease. Attempts to isolate a cytopathic virus and to transmit the disease by inoculation failed to demonstrate an infectious causal agent. An autoimmune response to normal nerve is suggested as the most likely aetiology amongst several alternatives. The heritability of IP is not established, but the disease has not been detected in a light Sussex flock maintained under similar conditions.