DOUBLE-STAINING SILVER-STAINED TISSUES. Ill 



The Hoggans' histological rings were described by me in - 

 the 1st edition of this work, p. 375, and in the Traite d. Meth. 

 Techn.j LEE et HENNEGUY, p. 138 ; so that I am in no way 

 responsible for the waste of time involved in this reinvention, 

 on the part of the inventor, and the editors of the Zeit. f. wins. 

 Mik., and other journals. 



202. Silver-impregnation of Marine Animals. On account of 

 the considerable quantity of chlorides that bathe the tissues 

 of marine animals, these cannot be treated directly with 

 nitrate of silver. 



HEETWIG (Jen. Zeit., xiv, 1880, p. 324) recommends fixing 

 them with a weak solution of osmic acid, then washing with 

 distilled water until the wash- water gives no more than an in- 

 significant precipitate with silver nitrate, and then treating 

 for six minutes with 1 per cent, solution of silver nitrate. 



HAEMEE (Mitth. Zool Stat. Neapel, v, 1884, pp. 44 to 56) 

 has discovered that many marine animals will live for some 

 time (half an hour) in a 5 per cent, solution of nitrate of 

 potash in distilled water. By washing them in this way, they 

 may be freed from the great part of their chlorides, and may 

 then be treated with silver nitrate in the usual way. This 

 method gave good results with Loxosoma and Pedicellina, with 

 Medusae, Hydroids, Sagitta and Appendicularia. 



VOSMAEE has been able by this means to demonstrate the 

 epithelium of Chondrosia and Thenea, which Sollas was unable 

 to see ; and MEYER has obtained good results with annelids 

 and ova of Teleostea. Few animals resist the action of nitrate 

 of potash so well as Loxosoma and Pedicellina, but die in the 

 solution in a few minutes. Their tissues, however, suffer but 

 little change and give good impregnations. Harmer thinks 

 that for these animals other solutions having the same density 

 as sea-water might be substituted for the nitrate of potash, 

 and recommends a 4' 5 per cent, solution of sulphate of soda. 



203. Double-staining Silver-stained Tissues. The nuclei of 

 tissues impregnated with silver may be stained with the usual 

 reagents, provided that solutions containing free ammonia be 

 avoided, as this would dissolve out the silver. These stains 

 will only succeed, however, with successful negative impreg- 

 nations ; as nuclei that have been impregnated will not take 

 the second stain. 



