CONNECTIVE TISSUE. 



153 



usually at the points of intersection.* In the meshes the basis-sub- 

 stance is in part homogeneous, in part traversed by delicate flbrillae. 

 Not infrequently a nucleated string passes directly into a bundle 

 of nbrillse. In the center of a mesh-space we encounter sometimes 

 a globular plastid, apparently isolated i. e., unattached to the 

 strings forming the reticulum. (See Fig. 52.) 



If we rub a stick of nitrate of silver over the surface of a 

 piece of a fresh umbilical cord, it will soon become brown 

 on exposure to daylight. Sections from such an umbilical 

 cord will show light, branching spaces in a dark brown basis- 



FIG. 53. UMBILICAL CORD OF A HUMAN FOETUS, NINE MONTHS OLD. 

 STAINED WITH NITRATE OF SILVER. 



S, light spaces, corresponding to the bioplasson cords in Fig. 52, branching and anas- 

 tomosing; B, dark brown basis-substance, indistinctly striated and granular. Magnified 

 500 diameters. 



substance. The light spaces correspond in size and shape to the 

 strings seen in specimens preserved in chromic acid. They anas- 

 tomose, and some of them send into the basis-substance smaller 

 branches, which often divide and subdivide so much as to show a 

 delicate, pencil-like appearance. The contours of the light spaces 

 and their branches are in many places serrated. The brown 



* In the umbilical cord of the pig-foetus the nuclei of the cord are much 

 more numerous than in the human. 



