1. Rumen bacteria were prepared in bulk from freshly killed sheep. They were exposed to ultrasonic disintegration and a preparation of cell walls was made by differential centrifugation.
2. The amino acid composition of acid hydrolysates of whole cells and cell walls was determined. Summation of these results shows that whole cells contained approximately 40% amino acids and cell walls approximately 30%.
3. A considerable proportion of the alanine content of cell walls was present as the D-isomer, partly ester linked as in teichoic acids and partly more tightly bound in ‘peptide linkage’ being released only after hydrolysis in constant boiling hydrochloric acid.
4. Cell walls were found to possess an alanine racemase which was inactivated only after incubation of the cell walls in 0.1 M-NaOH.
5. Whole cells contained approximately 8% carbohydrates and cell walls approximately 5%. The glucose and galactose contents of whole cells and cell walls were low, accounting for little more than 2% of the dry weight of the bacterial samples.
6. The amino sugar content of bacterial samples was approximately 3% and consisted mainly of glucosamine.
7. The total lipid content of rumen bacteria was approximately 25% and that of cell walls varied considerably between 10 and 23%.