1890.] MICROSCOPICAL JOURNAL. 149 



no^arzsi'i Delponte differs in having its uniform spines regularly arranged 

 as well as in its narrower sinus. SL saxonictati Buln differs in its rela- 

 tively broader isthmus and its shorter uniform spines. 



Fig. 38. — Xanthidinm brcbissonii Ralfs. This form differs from 

 that usually seen. 



Fig. 39. — Xanthidiiun aatlcaium Ehrb. 



A peculiar form of this is figured which some may think belongs to 

 another species by reason of the shape of the basal angles of the semi- 

 cells, still the spines are scattered in the same way as those of the species 

 under which it is placed. 



Fig. 40. — Art/irodcsmits octocor?//s Ehrb. 



A variety with wide and short cells. 



Staining and Permanent Preservation of Histological Elements 

 Isolated by Means of Canstic Potash or Nitric Acid.* 



By S. H. and S. p. GAGE, 



ITHACA, N. Y. 



" Properly chosen isolating reagents in the hand of a liistologist 

 form the best kind of a knife." Two of the most efhcient of these 

 are caustic potash and nitric acid. They dissolve or soften inter- 

 cellular substance and act more quickly on connective tissue than on 

 cell cement. The}' serve for isolating glandular elements, like gastric 

 glands, etc., or by prolonged action for isolating individual elements. 

 If the action is unchecked, both agents finally destroy all the cellular 

 elements also. 



CAUSTIC POTASH (POTASSIUM HYDRATE, KOIT) . 



1. Weak solutions destroy or dissolve all soft organic structures with 

 great rapidity. 



2. Strong solutions (30 to 50 per cent., also saturated solutions in 

 water) act with great rapidity on intercellular substances, and quite 

 slowly on the cellular or structural elements, so that the}^ iii'^y be iso- 

 lated and studied in their natural forms and relations. 



3. By the addition of water, glycerine, or alcohol to the caustic pot- 

 ash upon the elements the solution is simply weakened, when it rapidly 

 dissolves all the elements. 



4. The action of the strong solution maybe checked at anv time {a) 

 most satisfactoril}' by displacing it with a 60 per cent, solution of po- 

 tassium acetate, or (1^) by the addition of sufficient glacial acetic acid 

 to neutralize the caustic potash and form acetate of potash. After the 

 action of the caustic potash is checked, the elements may be preserved 

 indefinitely en masse in a 60 per cent, solution of acetate of potash, or 

 after being treated with a saturated solution of alum in 40 per cent, 

 alcohol or glycerine. 



5. A 30 to 50 per cent, aqueous solution — preferably a 35 to 40 per 

 cent, solution (caustic potash in sticks, 35 or 40 grams, water 51^ or 

 60 c.c.) — may be used for the isolation of the structural elements after 

 hardening the tissues with alcohol, cluomic acid, or a chromium salt, 

 picric acid, etc. It requires a longer time for the isolation of hardened 



•Abstracted from proceedings of the American Society of Microscopists, 1889, p. 34. 



