STRUCTURAL ORGANIZATION OF THE INITIAL LYMPHATICS IN THE MONKEY MESENTERY AND INTESTINAL WALL AS REVEALED BY AN ENZYME-HISTOCHEMICAL METHOD

The structure and distribution of the initial lymphatics in whole moun t preparations of the mesentery and intestinal walls of the Japanese m onkey (Macaca fuscata) were studied using an enzyme-histochemical meth od (KATO et al., 1991,1993). The lymphatic walls, colored dark brown b y their positive 5'-nucleotidase (5'-Nase) activity, were clearly dist inguished from the blood vessels (especially capillaries and arteriole s) which were colored blue due to their positive alkaline phosphatase activity. The specificity and localization of both enzyme reactions we re confirmed by comparative histochemical studies of the same specimen under a light microscope and scanning or transmission electron micros copes. Application of this staining method takes advantages of the ove rview preparation of flat membranous organs. The mesenterial area was generally lobulated in distribution with collecting lymphatics and blo od vessels. At about the center of each lobule enclosed by the vessels , 5'-Nase-positive initial lymphatics assumed tubulosacclar shapes, br anching antler-like figure to form dense networks in the main lymph va scular pathway. Their apical parts revealed marked knob-like blind end ings demarcated by a thin endothelial wall. No direct interconnection was recognizable between the lymphatic space and the tissue interstiti um as a prelymphatic fluid pathway. In such preparations, 5'-Nase-posi tive lymphatic islands could be found isolated from the lymphatic netw ork.