Bacterial flora of the gastrointestinal tracts of CF#1 and DDD mice aged 4 to 5 weeks were examined qualitatively and quantitatively.
Lactobacilli and yeasts were detectable from contents of the stomach as well as the upper and lower parts of intestine, whereas enteric bacteria, streptococci, staphylococci and bacteroides mainly from those of the lower intestine (Tables 1 and2) . These findings are in agreement with the data described by Dubos et al. [1, 12, 13, 14] and Smith [15, 16] . Dubos et al. [1, 14] described that most of lactobacilli, yeasts and fusiform bacilli might be attached so close to the gastrointestinal wall that they could not be washed out by repeated washings. The fact was corroborated partly by the present observations; after washing in phosphate buffer saline with violent agitaion, a large number of lactobacilli and yeasts were recovered in the homogenates of the gastrointestinal wall (Table 5) .
The data, except for those of small intestine, were analyzed statistically for studying the relation between the fecal and the gastrointestinal flora. No significant differences were shown in between the fecal and the rectal counts, nor between the fecal and the cecal counts of enteric bacteria. Variance analysis on the counts of streptococci, staphylococci and bacteroides also gave similar results to those of enteric bacteria. With the counts of lactobacilli or yeasts, no significant differences were observed between the feces and the rectum, cecum or stomach. On the other hand, with the counts of enteric bacteria, the regressions of the rectum or cecum on the feces were significant. The regression tests on the counts of streptococci and staphylococci gave the results similar to those concerning enteric bacteria. With the counts of bacteroides, regression of the rectum on the feces was significant, whereas that of the cecum on the feces was not significant. With the counts of lactobacilli, regression of the rectum on the feces was significant, but the regression of the rectum or stomach on the feces was not. On the fecal count of yeasts, regressions of the rectal, the cecal and the gastric counts were significant (Table 3) .

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