On the Reticular Tissue and Lattice=fibers occurring in the Milk=spots of Omentum. By Dr. Yukio Hamazaki. From the Pathological Department of Okayama Medical College (Director: Prof. Oto Tam ura). 2 Figures (Plate III) and 3 Text Figures. Ranvier and Weide n reic h regarded the omentum as a flattened- out lymph gland and the abdominal cavity as its lymph sinus. The latter, furthermore, theoretically emphasized that the omentum is nothing but a sheet of reticular tissue, the "taches laiteuses" correspond- ing to the secondary nodules. Lately, Kiy ono agreed with the above view, though lie pointed out that the histiocytic cells in the milk-spots do not form reticular tissue, unlike those in the lymph glands. At the Fifteenth Pathological Congress of Japan (1925) I reported that the milk-spots in the rat, cattle, and pig are provided with a certain kind of reticular tissue. The purpose of the present paper is to settle this problem using specific stainings for the reticular fibers and for the lattice-fibers ("Gitterfasern" of v. Kupffer), which may be in an intiniate relation with them. Material and methods. The material was obtained from the cattle, pig , dog, cat, rabbit, guinea-pig, rat, mouse, chicken and human subject. As the control the organs containing reticular tissue, i. e., lymph glands , spleen and thymus gland were also examined. The material fixed with 10% solution of lormalin was studied as stretched specimens and as sections . For reticulum-staining the eosin-methyl blue method modified by the author was used: 1. Sections are stained for 30 minutes in 1% solution of eosin (a few drops of glacial acetic acid is added to 100 cc of the solution) . Then they are washed with distilled water . 34 Yukio Hamazaki, 2. They are rinsed in 1% solution of phosphomolybdic acid for a few seconds and washed with distilled water. 3. They are stained with 0.1% solution of methylblue for five minute's and then washed with distilled water. 4. They are differentiated and dehydrated in 95% alcohol, keeping them in constant motion, so as to obtain uniform decolorization. 5. Finally they are mounted in balsam, passing through absolute alcohol and xylol. In sections thus treated, reticular fibers are stained green, the nuc- lei of the reticular cells violet-red, those of the wandering histiocytes violet and cytoplasm blue. The nuclei of lymphocytes are stained red, the erythrocytes orange-red. The lattice-fibers were studied with the Bielschow sk y-Maresch 's impregration method. In some cases of rat material vital staining with lithium-carmine was performed prior to eosin-methylblue method and the Bielscho w sky's method to make clear the relations of the histiocytes and reticulum. Experiments. As is well known, the "Wiles laiteuses," are best developed in the omentum of rat. In this paper the reticular and lattice-fibers of this form, especially in its follicular milk-spots, will he dealt with. Reticular fibers. Rat. Inthe stretched specimens one can clearly see that many connective tissue fibers supporting the net-trabecules of the omentum go into the milk-spots. The fibers ramify into several branches, thus dividing the milk-spots into many lobales. Since the milk-spots of rat are crowded with many cell-elements, it is very hard to make out the relations of the collagenous fibers to the reticular ones or to the cells. In horizontal sections, one can distinguish three layers in the milk- spots. The outer layer is composed of many wandering histiocytes, mast- cells and some lymphocytes, polymorphonuclear leucocytes. In this region the reticular cells are scattered over in a small number and the fiber-elements are poorly developed. The reticular cells are either spindle- shaped or stellate. The meshes are relatively large, measuring about 17p in diameter and accommodating many wandering cells mentioned above. The cell-body of the wandering histiocyte in the meshes contains a On the Reticular Tissueand Lattice-fibersoccurring in the Milk-spotsof Omentum. 35 delicate net-apparatus consisting of very fine fibrils. Each cell is con- nected with the neighboring ones by means of fibril-bridges which arise from the net-apparatus. The mast-cells also have fine net-apparatus in the cytoplasm, though they produce no fibril-bridges. In the intermediate layer the reticular cells with round or oval nuclei (about 62) are present in large numbers. They are triangular or stellate in shape. The cytoplasmic processes with fiber-element are gentrally short and form small reticular meshes (about 15/2 in diameter) and accordingly they can accommodate only few wandering cells. The wandering cells mainly consist of lymphocytes and histiocytes. In this area the fibril-bridges between the histiocytes are not so well developed as compared with those of the outer layer. The reticulum in this region resemble very much that of the splenic pulp (red pulp) or of the lymph- sinus. In the inner layer the reticular cells with flattened or triangular nuclei (about 6p) are present in a relatively small number, but time fibers are numerous, long and tortuous forming reticular meshes of somewhat polygonal shape (about 30p in diameter). The meshes are filled with many lymphocytes. The reticular fibers are connected with the adventitial fibers of blood-vessels, which are chiefly distributed in the intermediate layer. The reticulum in this layer closely resemble that of the splenic nodule (white pulp). The vital staining with lithium-carmine was followed after fixation by eosin-methylblue to investigate the relations of the histiocytes and the reticulum. Lately, Fahr studied on the lymph glands at the hilus of the liver and he recognized very many epithelioid cells are developing from the reticular cells. He inferred that these epithelioid cells belong to the histiocytes of Ascho ff and K iy o o. In my material the change process of the reticular cells into wandering histiocytes could be clearly brought out. The stellate cells of the reticulum shorten their processes, become more and more spherical and finally set themselves free from .the reticulum. The color of carmine-granules turn into blue-violet by methylblue. A small number of such granules are present in the reticular cells. The granules increase in number as the cells become more spherical and detatched from the reticulum. (Fig. 1, Plate III) . Guinea-pig and mouse. The milk-spots of these two forms are similarly constructed as those of the rat but the cell-elements, especially the lymphocytes , are less than in the rat. Cattle and pig. 36 Yukio Hamazaki, In the milk-spots of the cattle the reticular cells are mostly stellate in shape. The cytoplasmic processes of the superficially disposed cells are relatively short, but in the deeper part of the milk-spots such processes become gradually long and slender, forming a medium-sized meshes. Iii the cytoplasmic processes many tortuous and anastomosing fibrils can be detected, but they show little tendency to form the true reticular fibers, unlike those of the rat. In the reticular meshes some large and small mononuclear wandering cells, lymphocytes and eosi- nophils are situated. These pectures resemble very much the sinus- reticulum of lymph glands. In the milk-spots of pig, however, the fiber- elements are somewhat well developed. Chicken. The milk-spots of chicken are chiefly developed in the superficial part of the mesentery. The subserous connective tissue buried under the milk-spots') send off many collagenous fibers into them and the fibers are divided into several branches anastomosing with the reticular fibers. The reticular fibers reach the outer-layer of the milk-spots where they branch into fine fibrils and become connected with the net-apparatus in the cytoplasm of the large mononuclear wandering cells. The reticular meshes are relatively large sized and lodge various kinds of wandering cells. Man and (log. The milk-spots of man are divided into several lobules by sinusoid spaces whose branches go into the central part of the lobules. The spaces conmunicate with the perivascular lymph-spaces. The wall of the sinusoid space is composed of endothelioid cells, the appearances of which are quite similar to the reticular cells. Some of their processes are wedged into the cell-elements of the milk-spots. In the parenchyma the reticular cells are scattered over in a small number and their fine fibers surrounding each wandering cells are connected with the collagen- ous fibers which come from the subserous connective tissue. The reticulum in the milk-spots of dog resemble that of man, but the sinusoid space can not so clearly be made out. The solitary milk-spots developed on the peritoneal surface are composed of large mononuclear wandering cells as in the outer layer of the milk-spots of rat. Each wandering cell sends out fine fibrils which anastomo,se with those of neighboring cells. Some of these fibrils are fused to form reticular fibers. Rabbit and cat. The milk-spots are mainly composed of large mononuclear cells. Many connective tissue fibers go into the milk-spots from the net On the ReticularTissue and Lattice-fibersoccurring in the Milk-spotsof Omentum. 37 trabeoules of the omentum and so the reticular . fibers are hardly differentiated from the collagenous fibers. Lattice•fibers. In the milk-spots of rat impregnated with the Bi el s c ho wsk y- Mar es ch's method the wandering histiocytes of the outer layer stain themselves in a light brownish color and their nuclei in a deep brown. The cell-boundaries of the histiocytes are somewhat clearly made out. In the deeper area, however, cell-bodies are generally stained diffusely in a light gray and their boundaries being blurred. The nucleus of the reticular cell (histiocytic cell) is colored deep gray, while that of lympho- cyte black.