ORIGIN OF COLORED BLOOD-CORPUSCLES. 107 



with almost exclusively in the earliest stages of development of the embryonal 

 connective tissue, and in transient foetal organs, such as the umbilical cord 

 and placenta. This tissue appears in two varieties : first, in the shape of a 

 protoplasmic reticulum of greatly varying size, with nuclei at its points of 

 intersection, the meshes of which hold the jelly-like mucoid basis-substance 

 (umbilical cord). In the centers of the meshes, globular and apparently 

 isolated bodies are seen. The other form consists of a delicate fibrous 

 reticulum, having oblong nuclei at the points of intersection, the meshes 

 being filled with single protoplasmic bodies (so-called " decidua cells" of the 

 placenta), or with a mucoid basis-substance with scanty bodies (derma and 

 mucosa of the embryo in the earliest stages). 



Recent researches have proved that this mucoid basis-substance is not a 

 structureless mass, but that it is pierced by a living reticulum, which is 

 continuous with a smaller net-work pervading all protoplasmic formations. 

 As the fibrous reticulum of myxomatous tissue is a protoplasmic formation, 

 its fibers, too, contain a fine reticulum of living matter, which is also con- 

 tinuous with the fine reticulum of its neighbors. So the basis-substance, in 

 either its mucoid or fibrous variety, differs from protoplasm only by a chemi- 

 cally altered substance within the meshes. This substance in the protoplasm 

 is a liquid, in the basis-substance a semi-solid, though not strictly glue- 

 yielding mass. 



As has been known for a long time, comparatively low powers, when 

 brought to bear on the adenoid tissue, demonstrate the presence of a delicate 

 fibrous reticulum, which at the points of intersection is generally slightly 

 thickened and flattened so as to present a plate-like appearance. 



These intersections are sometimes provided with nuclei, and the meshes 

 of the net-work are always filled with lymph-corpuscles. Although these cor- 

 puscles are so closely packed that they often flatten each other, still each one 

 is generally separated from its neighbors by a narrow, light substance which 

 is probably liquid. 



Unless the lymph-corpuscles be torn apart by mechanical injuries, such as 

 cutting, washing, etc., etc., they are all connected with each other by ex- 

 tremely delicate, grayish spokes, which traverse the intermediate substance 

 in all directions. A like connection always exists between the lymph- 

 corpuscles and the fibrous reticulum nearest to them. 



Most authors claim that this fibrous reticulum of the adenoid tissue is 

 structureless, and exhibits nuclei only at its points of intersection. This 

 assertion must be based on Canada balsam specimens, for it makes all minute 

 details fade away. My own specimens, cut from fresh lymph-ganglia, or such 

 as had been preserved in a dilute solution of chromic acid, show a well- 

 marked net-work in the fibrous reticulum, both in the unstained and in the 

 carmine specimens. 



While we are on this subject of the preparation of specimens, let me say, 

 once for all, that if we hope to see the minute structure of this tissue, our sec- 

 tions must be cut from fresh or from chromic acid preparations, for alcohol or 

 water destroys the details. If stained at all, it should be done with carmine, 

 or, what is better, the one-half per cent, of chloride of gold. This last-named 

 agent has a peculiar faculty for taking hold of the living matter of the most 

 minute organisms and making it stand out in a very satisfactory manner. 

 Lastly, I would state that glycerine seems to be the only mounting substance 

 now known that will preserve tissues absolutely unchanged. 



