The ecological behavior of Clostridium perfringens in the human intestine was investigated by using a quantitative method for bacterial count. C. perfringens was found in all the fecal specimens from healthy persons and in almost all the contents of the large intestine of corpse. The actual number of the organisms ranged from 10¹ to 10⁹ per g of feces. The heat resistant C. perfringens was detected in about half of the fecal specimens heated at 100C for 60 min, and the number were less than 10⁶ per g of the feces. The resistant organisms seemed to be a permanent inhabitant in some persons. Using the Hobbs' factor sera (Types 1 to 13), the serotypable strains were frequently found among the isolates from the heated specimens, and two or more serological types were often found in single specimens. On the other hand, changes in serotypes in a person were observed by repeated examinations.
The behavior of C. perfringens in the colon and ileum of the corpse were similar to that in fecal specimens from healthy persons. However, C. perfringens were isolated from the jejunal contents of only 3 out of 12 corpses. All the isolates from jejunum were heat sensitive and three of them were agglutinated by Hobbs' factor sera.
The toxinogenicities (κ and θ) of the untypable isolates were dependent on the temperature of heating used for isolation, while those of the typable ones varied independently of the temperature.