SILVER METHODS 



316 



SILVER'S 



may be briefly filled with y*5 strength 

 hydroquinone solution after the silver 

 has been thoroughly washed out and 

 before fixation. Stains such as Mayer's 

 paracarmine may be used. When the 

 silver is thus applied for but an instant 

 it does not involve the underlying 

 endothelium or reticulin fibers. In 

 thick sections the silver-line network 

 of the bronchial epithelium may often 

 be followed directly into that of the 

 alveolar walls, and the two are then 

 seen to form one system. On the 

 alveolar walls the areas circumscribed 

 by the meshes of the net are not uni- 

 form. The smaller, more heavily 

 marked, meshes enclose alveolar wall 

 cells (pneumonocytes, septal cells, etc., 

 which see) while the larger meshes, 

 known as bare areas, contain no surface 

 cells. Around them the lines in some 

 animals, as rabbit, are often incomplete. 

 Silver Methods. General statement. A 

 brief historical review by Silver, M. L., 

 Anat. Rec, 1942, 82, 507-529 shows that 

 progress has been made in the control 

 of these techniques to the point where 

 they yield reliable results with con- 

 siderable uniformity. Impregnation of 

 blocks of tissue and reduction of the 

 silver in various ways were and still are 

 the bases of the methods of Golgi, 

 Cajal and Bielchowsky which have 

 contributed so much to our knowledge 

 of the Nervous System, which see. 

 But one had to wait until the sections 

 were cut and examined to ascertain the 

 results. Sometimes they were all that 

 heart could desire; at other times the 

 worker faced repeated disappointments. 

 Having labored with the silver impreg- 

 nation of neurofibrils I have always 

 avoided silver methods whenever others 

 can be employed in their place. Now 

 however with the successful application 

 of reduced silver to sections mounted 

 on slides the technique is brought 

 from the insides of the blocks of tissue 

 which one cannot see into the open, 

 thanks to Rogers, W. M., Pappenheimer, 

 A. M.,and Goettsch, M., J. Exp. Med., 

 1931, 54, 167-169. Another advance 

 was the introduction of protargol as the 

 silver salt for treating sections of the 

 central nervous system by Bartelmez, 

 G. W. and Hoerr, N. L., J. Comp. 

 Neurol., 1933, 57, 401-428. Then, like- 

 wise in Bensley's laboratory, Bodian, 

 D., Anat. Rec, 1936, 65, 89-97 employed 

 protargol with hydroquinone as reducer 

 and speeding up results by copper, 

 mercury and acid. Finally Davenport, 

 H. A., McArthur, J., and Bruesch, S. P., 

 Stain Techn., 1939, 14, 21-26 dispense 

 with copper, and, by combining pro- 

 targol and silver nitrate at optimum pH, 



reduce staining time of sections of pe- 

 ripheral nerves to 2 hrs. In addition, 

 Silver (loc. cit.) by well planned experi- 

 ments has shown that staining with 

 silver is brought about through adsorp- 

 tion and flocculation of electrically 

 charged silver micelles by suitably 

 charged surfaces. When these newer 

 methods are widely brought to bear 

 upon tissues of the body in normal and 

 pathological conditions a significant 

 service will be performed. Suffice it 

 here to give a few details under Nervous 

 System, Spirochetes, tests for Calcium, 

 Chloride, Vitamin C, Reticular Fibers, 

 Melanin, etc. 



It is in some cases desirable to destain 

 silver slides. To do this pass down to 

 running water for 5 min. and treat sec- 

 tions with 0.25% aq. potassium per- 

 manganate to which 1% of cone, sul- 

 phuric acid is added for 15 min. Wash 

 in running water 2 min. Bleach in 5% 

 aq. oxalic acid 2-5 min. Wash. Re- 

 peat the stain omitting preliminary 

 oxidation-reduction, or apply some 

 other technique (Wilson, R. A. J., Am. 

 J. Clin. Path., 1943, Tech. Suppl. 7, 39). 



Silver Nitrate is employed in many tech- 

 niques. It is important to remember 

 that ammoniacal silver nitrate solutions 

 on evaporation yield an explosive com- 

 pound. Consequently solutions of this 

 sort should never be allowed to dry but 

 should be washed down the sink with 

 plenty of water. 



Silver Staining of bone (McCollum, E. V., 

 Simmonds, N., Shipley, P. G. and 

 Park, E. A., J. Biol. Chem., 1922, 51, 

 41-49). 



Silver's rapid silver-on-the-slide method 

 for nervous tissue (Silver, M. L., Stain 

 Techn., 1942, 17, 123-127). A new 

 feature of this technique is the reducing 

 solution. 



1. For nuclei, fine fibers and nerve 

 terminals, fix with 10% neutral or 

 commercial formalin in 1% aq. sodium 

 chloride with Bouin's fluid or with some 

 other fixatives which he specifies prefer- 

 ably by Perfusion. 



Cut frozen sections 10-40/x or dehy- 

 drate slowly, imbed in paraffin or cel- 

 loidin and cut 2-20^. Mount paraffin 

 sections on slides and deparaffinize in 

 the usual way. In the case of celloidin 

 sections remove celloidin with several 

 changes acetone and of equal parts 

 absolute alcohol and ether and pass down 

 through alcohols to water. 



To make reducing solution dissolve 

 64 gm. Rochelle salts (potassium sodium 

 tartrate) in 500 cc. aq. dest. Boil vigor- 

 ously. Add 10 cc. 10% aq. silver nitrate 

 and boil again at least 5 min. Remove 

 from flame. Add 0.3 gm. crystalline 



