150 THE AMEEICAN MONTHLY [July, 



than of fresh tissue, and the results are not so satisfactory. The ele- 

 ments of ahiiost any tissue may be successfully isolated by means of 

 strong solutions of caustic potash, but it has been most successfully em- 

 ployed in the study of the epidermal and muscular tissues, especially 

 the elements of cardiac and smooth muscular tissue. 



6. When fresh tissues are employed it is especially necessary that 

 they be perfectly fresh, and that, if from organs like the heart, where a 

 great deal of blood is present, the blood should be washed away with 

 water before the application of the reagent, as the strong caustic 

 potash preserves the blood corpuscles, and their presence is detrimental 

 to the clearness of the outline of the elements. 



7. Only small pieces of tissue should be used (if the tissue is mas- 

 sive the pieces should not exceed half a cubic centimeter), and about 

 fifteen to twenty times as much potasli solution should be used as tissue. 



8. After ten to fifteen minutes the tissue should be tested with dissect- 

 ing needles every five minutes, in order not to prolong the action un- 

 necessarily. 



9. As soon as the elements separate readil}', the caustic potash is 

 poured off and a plentiful supply of a 60 per cent, solution of acetate 

 of potash added (potassium acetate 60 grams, water 40 c.c.) . This 

 displaces the caustic potash and checks its action. The efliiciency 

 and rapidity of the action of the acetate is increased by the addition of 

 I per cent, of glacial acetic acid to it. 



10. After the caustic potash has been removed the elements may be 

 mounted for the microscope in 60 percent, acetate of potash, in glycer- 

 ine or in glycerine jelly. 



11. Staining and mounting the isolated elements: After the caustic 

 potash has been displaced the acetate of potash is removed, and a plen- 

 tiful supply of a saturated aqueous solution of alum is added and 

 allowed to remain for a considerable time, preferably twenty-four hours 

 or more. The elements then stain very satisfactorily with haamatoxylin 

 or alum carmine. Other stains may also be successfully used. After 

 staining, the elements maybe mounted by any of the approved methods 

 — in glycerine, glycerine jelly (which is perhaps the best), Farrant's 

 solution, or Canada balsam. After the use of the alum water, the ele- 

 ments may be preserved en masse in 40 per cent, glycerine or 40 per 

 cent, alcohol, stained and mounted whenever desired. 



If the preparation is left in acetate of potash for a day or more, the 

 cells stain well with alum carmine, or haematoxylin without using the 

 alum water. It is necessary, however, to wash away the acetate 

 quickly with water, or simply to absorb it, otherwise there will be a 

 multitude of crystals in the preparation. The use of alum water for 

 the cardiac muscles of the frog is not so successful as with those of 

 mammals. vStaining directly from the acetate is quite successful. 



NITRIC ACID (aCIDUM NITRICUM, HNO3). 



I . Nitric acid in various decrrees of concentration has been used for 

 the isolation of the structural elements by many difierent histologists, 

 but it is due to Paulsen that a 20 per cent, solution (strong nitric acid 

 20 c.c, water 80 c.c.) came into general use ; and while it serves fairly 

 well for many of the tissues, its greatest applicability is to the isolation 

 of the structural elements of muscular tissue, especially the ordinary 



