The microorganisms associated with the undiseased human colon wall were examined in material obtained from four sudden-death victims. In traffic accident subjects (aged 45 and 16 years) the anaerobe-aerobe ratio was about 10 4 :1 in all areas of the colon examined, whereas in acute heart failure subjects (aged 74 and 46 years) the ratio was as low as 1.2:1. The flora of each individual was distinct and complex. Although the predominant anaerobes isolated were Bacteroides and Fusobacterium spp., which composed over 50% of the flora in some samples, the species isolated (indicated by morphology and glucose fermentation products) varied between individuals. Other major types observed were gram-positive nonsporing rods, including Bifidobacterium spp., and anaerobic cocci (between 8 and 20% of isolates). Clostridia were only isolated in significant numbers from one individual. Scanning electron microscopy showed that most of the organisms were present below the top surface of the mucin layer overlying the mucosa. The use of several different preparative procedures for microscopy showed a complex microbial structure within the mucus, but major variations in the bacterial populations in different areas of the colon were not found. Spiral-shaped organisms up to 60 μm long in the form of double helices were found in two subjects by scanning electron microscopy but were not isolated during the parallel bacteriological investigation. The differences between this and previous studies are discussed in relation to experimental procedures and also in contrast to results with animals that showed a particularly specialized flora associated with the colon wall.

Gram negative budding bacteria with a characteristic morphology have been observed in the caeca of chickens, turkeys, ducks and guinea fowl at levels between 0–4 and 24% of the total flora. Using strict anaerobic techniques a detailed study has been made of the organisms isolated from the caeca of chickens aged between 15 and 44 d. The majority of isolates were identified as Gemmiger formicilis, the strains being divided into twomajor types according to the relative amounts of butyric acid and lactic acid produced from glucose. A second group of isolates could not be related to any known species. Amongst properties of ecological interest studied were limiting temperatures for growth, ammonia utilization, ability to utilize various carbon sources and survival in environments outside the intestine. Attempts to produce a selective medium for the isolation of these organisms when present at less than 2% of the total flora were unsuccessful.