APPENDIX. 377 



b. Filter fresh lemon-juice through flannel and place 

 the tissue in the ITtrate for about 5 minutes before 

 placing it in gold chloride. After treatment with 

 gold chloride, wash the tissue well with water and 

 expose to light in the ordinary way in acidulated 

 water, or place in formic acid in the dark as in (a). 

 (Ranvier.) 



c. The tissue after treatment with gold chloride is 

 washed and placed in distilled water for 6 to 20 

 hours until it is of a steel-grey colour ; it is removed 

 to a saturated solution of tartaric acid for about 10 

 minutes and then warmed in the solution up to 

 40 50 C. until it becomes dark ; this generally 

 takes about ten minutes (Klein). If it is desired to 

 stain the tissue more quickly, it may be left in the 

 gold chloride solution for about three-quarters of an 

 hour, then well washed and at once treated with 

 tartaric acid as above. 



Silver Nitrate. 



For the method of using this cp. Less. xu. A, 2, C, 4, 

 and Less. xvm. C, 1. It serves mainly to trace out 

 flat tesselated epithelium, such as that of arteries, 

 veins, or lymphatics. By exposure to light, the silver 

 is reduced ; in a fresh tissue that has been placed in 

 nitrate of silver, the reduction on exposure takes place 

 more readily in the homogeneous substance between 

 the cells or * cement substance ' than in the cells. 



As a consequence, where there is a single layer of cells, 

 with a small amount of cement between them, the 

 reduced silver in this substance marks very distinctly 

 the outline of the cells. 



