Abstract
On comparing germ-free and conventional rats, inactivation of the tryptic activity was found to take place in the caecum of conventional adult rats only. A microbial intestinal inactivation of the tryptic activity was established in suckling conventional rats within 10 days after birth. At 3 weeks of age, suckling germ-free rats were found to have less faecal tryptic activity than their early-weaned littermates.