STAINING REAGENTS. 



77 



chlorides, and place it in a dilute solution of the reagent (J-J-J per 

 cent.). The tissue soon 5-10 minutes becomes white, and as 

 soon as it looks grayish remove it and wash it in distilled water. 

 Place it in ordinary water, and expose it to good daylight, when it 

 rapidly becomes brown. It can then be preserved in spirit until it 

 is required. 



A membrane may be stained in situ, e.g., the central tendon of 

 the diaphragm of a rabbit, or the mesentery, e.g., of a frog. Open 

 the abdomen, irrigate _ === _ 



the membrane by allow- ^^s^ .^^L B 



ing distilled water to 

 fall on it from a pipette. 

 This removes all sub- 

 stances that might com- 

 bine with the silver and 

 give rise to illusive ap- 

 pearances. Drop on the ^j'-i^HJ^ "" Wf W C 

 silver solution by means 

 of a pipette. Treat t-he 

 membrane as in the 



FIG. 45. A. Vulcanite rings used for stretching a mem- 

 bratie which is to be silvered ; B. Conical rings, the 

 one inside the other ; C. A single ring. 



previous case. 



2. Negative Method 

 (Recldingh ausen). This 



is the usual method by which the intercellular cement substance is 

 stained black a weak solution being used as for the study of 

 endothelium. The membrane 

 ought to be kept stretched, 

 e.g., over the mouth of a 

 porcelain capsule. 



The following modification j, 

 is recommended by Thanhoffer, 

 and it works well. After the 

 membrane is exposed to the w ' 

 action of silver nitrate, it is 

 washed with a 2 per cent, solution of acetic acid. 



3. Positive Method (77^-) is specially designed for showing lacunae 

 and lymphatic cavities, e.g., the lymphatics of the skin and cornea. 

 Place the tissue for several hours in i per cent. AgN0 3 in the dark, 

 wash in water, transfer in dark to 3-5 solution of sodic chloride. 

 Wash in water, expose to light. The spaces are found fdled 

 with black granules. Examine in glycerine. 



Sometimes silver nitrate is us"ed in a solid form, e.g., for the 

 cornea. This will be referred to afterwards in treating of the cell- 

 spaces of the cornea itself. (Lesson on Eye.) 



Silver preparations show the cement substance of epithelium 



