EPITHELIAL AND ENDOTHELIAL TISSUE. 317 



structure is easily recognized in each ribbon, in both fresh speci- 

 mens and those preserved in a solution of chloride of gold or 

 chromic acid. The nature of the cement-substance between the 

 ribbons is made apparent by treatment with a solution of nitrate 

 of silver, which colors it dark brown, and at the same time leaves 

 delicate, light, conical lines unstained, as is the case in all other 

 formations of cement-substance. (See Fig. 135.) 



The connecting filaments in the cement-substance, owing to 

 their extreme delicacy, are often imperceptible in fresh prepara- 

 tions, and even in specimens preserved in chromic acid some- 

 times only a delicate granulation is visible in their place. To 

 render these filaments distinct, the staining with a one-half per 

 cent, solution of chloride of gold must be resorted to. Epithelial 

 formations are, as a rule, very slowly colored by the gold-salt, as 

 the ensheathing envelope of the cement-substance seems to inter- 



8~$0&^^ 

 FIG. 135. RIBBONS OF THE CRYSTALLINE LENS OF A BULLOCK. 



F, isolated nucleated ribbon of reticular structure, and with fringed edges ; C, two ribbons 

 separated by the light cement-substance, interconnected by delicate conical filaments ; S, two 

 ribbons, stained with nitrate of silver ; the cement-substance dark brown, pierced by light 

 lines. Magnified 600 diameters. 



fere with the action of the . re-agent on the bioplasson reticulum 

 in the interior. But the conical filaments in the cement-sub- 

 stance, if exposed to the re-agent for twenty to forty minutes, 

 assume a violet color, and are rendered clearly visible. 



The cloak of cement-substance is not of uniform hardness ; 

 it is probably more liquid in some places than in others, as indi- 

 cated by the observations of J. Arnold, who drove colored injec- 

 tion liquids into the middle of the cement-substance. According 

 to Thoma, an indigo-carmine solution being brought in repeated 



