1. A new technique has been used to study the fermentation of hemicellulose and α-cellulose in vitro. This involved the use of 14C-labelled carbohydrates fermented in the presence of normal herbage material in an artificial rumen.

2. A method of growing grass in an atmosphere of 14CO2, its fractionation into hemicellulose and α-cellulose and the analysis of the labelled V.F.A. end-products are described.

The data collected during 26 days of cattle watching have been examined. Differences in the distribution of the habits, and of the length of time spent on each habit, larger than those recorded by other workers, are given. Possible explanations for these differences are discussed; part of the variations may have been caused by individual behaviour, and part by changes in climatic conditions. It is concluded that the major cause of variation is the difference between the herbage quantity and quality on the different pastures.