114 



THE ESSENTIALS OF HISTOLOGY. 



posed only of flattened epithelium-cells (fig. 139) continuous with those 

 that line the arteries and veins ; these cells can be exhibited by staining 

 a tissue with nitrate of silver. The capillaries vary somewhat in size 

 and in the closeness of their meshes ; their arrangement in different 

 parts, which is mainly determined by the disposition of the tissue- 

 elements, may best be studied in injected preparations, and will be 

 described when the structure of the several organs is considered. 



FlG. 138. A SMALL ARTERY, A, AND VEIN, V, FROM THE SUBCUTANEOUS CONNECTIVE- 

 TISSUE OF THE RAT, TREATED WITH NITRATE OF SILVER. (175 diameters.) 



i, a, endothelial cells with b, b, their nuclei ; m, m, transverse markings due to staining of 

 substance between the muscular fibre-cells ; c, c, nuclei of connective-tissue corpuscles 

 attached to exterior of vessel. 



In the transparent parts of animals, the blood may be seen flowing 

 through the capillary network from the arteries into the veins. The 



