Changes from birth to maturity in the pattern of distribution of lactase and sucrase activity in the mucosa of the small intestine of pigs.

I . Measurements were made of changes in lactase and sucrase activity of homogenates of small intestine mucosa of sixty-one pigs varying in age from newborn to mature animals. 2. From each pig, samples for enzyme determination were taken from siu sites along the small intestine. These sites were at 5,20,40,60, 80 and 95 yo of the length of the small intestine, measured from the pylorus. 3. Lactase activity was present at high levels in the newborn pig, the maximum being found at the 20 % site. Between birth and 8 weeks of age there was a fall in the amount of activity in the mucosa of the small intestine. In older pigs the levels of mucosai lactase activity were not greatly different from those found in 8-week-old pigs, although the distribution along the small intestinc tended to change with advancing age. 4. Sucrase activity was found only once in thirty-six samples from the small intestine of six newborn pigs, but was present in all six pigs sampled at I week of age. Levcls of activity continued to rise until maturity. Maximum activity was found at the 20 or 40 % site in the younger pigs (1-8 weeks of age). In the older pigs, high activity was found at a wider range of sites, the peak of activity generally being at the 40 and 60 y/o sites.