SUMMARY: When metabolizing glucose or other fermentable sugar in vitro at a temperature 8-12" below the normal rumen temperature, three species of rumen holotrich ciliates were liable to exhibit highly abnormal appearances which were not seen a t 35-38'. These abnormal appearances consisted essentially in a contraction and fusing together of the bulk of the storage polysaccharide (amylopectin) granules into a narrow central zone in the endoplasm. The outer clearer endoplasmic region, however, still contained numerous discrete granules in Isotricha prostoma and I . intestinalis but not in Dasytricha ruminantiurn. The abnormality was not quickly lethal to the organisms and appeared not to involve any alteration in shape or position of the macro-nucleus. The presence of nunen liquor, with all its soluble constituents but not necessarily its bacteria, is required for a high incidence of abnormality and the organisms should also initially contain but little storage polysaccharide. Evidence is presented in favour of the view that the abnormalities are connected with the utilization (auto-fermentation) of storage polysaccharide rather than with its synthesis. Nevertheless, the abnormalities cannot be induced in Isotricha when starch grains (vegetable or protozoan) have first been ingested.When harvesting in quantity from sheep rumen contents the holotrich ciliates (i.e. a mixture of Isotricha prostoma, I. intestinalis and Dasytricha ruminantiurn) by a labour-saving and apparently quite reproducible modification of the glucose-fermentation methods of Masson & Oxford (1951) and Heald & Oxford (1958), we noted in our washed suspensions what seemed to be the sporadic and unpredictable appearance of a relatively few highly abnormal but still living ciliates. Furthermore, the kind of abnormal appearance in the Isotricha organisms was not exactly the same as in the Dasytricha organisms, although a marked contraction of internal contents was a feature in each. This paper records our observations on: (a) how to prevent these abnormalities from occurring; (b) how to ensure their appearance in a large percentage of living ciliates in the culture; (c) the nature of the functional derangement which can bring about such abnormal appearances in still living organisms. METHODS

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