The nutrition of ruminants is intimately connected with microbial digestion in the rumen. Because a substantial proportion of the diet ultimately utilized by the animal exists as bacterial substance for a time, the fate of the bacterial cell in the alimentary tract is of interest. We are at present investigating the possible significance of the bacterial cell wall in the nutrition of the sheep as such walls constitute from 10 to 30% of the dry weight of the cell and are known to contain carbohydrate (1). As a part of the investigation a general survey by electron microscopy of bacterial types present in rumen contents was made. Phage particles both free and attached to cells were found to be present. Many empty bacterial cell envelopes and fragments of cell walls were also found.