The surface area of the intestinal mucosa in the lactating rat.

1. The mucosal and serosal surface dimensions of the rat duodenum, jejunum and ileum were obtained by measurement of photographs of histological sections. The surface areas were calculated from these data.2. Measurements were made on the intestines from virgin rats and from rats on the sixteenth day of lactation. The mucosal area/unit length of serosa was appreciably increased in all parts of the intestine during lactation. The mucosal area/serosal area (MA/SA) ratio was also markedly increased, but to a lesser extent distally, where an important component of the intestinal hypertrophy was dilatation of the intestine.