160 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Such preparations show the fibres dark reddish browu on a light red, 

 bluish, aud oveu luistaiued ground. The most euuvcuient hardening 

 fluid is 2^ parts bichromate of potash, 1/2 sulphuric acid, to 100 parts 

 of water. 



Method for the Sliver Staining of Marine Objects.* — The prin- 

 ciple of this method was suggested to Mr. S. F. Ilarmcr by Dr. W. H. 

 Ransom, and consists in the replacement of distilled water in the 

 ordinary process of silver staining by a solution of a neutral salt not 

 preeipitable by silver nitrate, aud of the saiue specific gravity as sea- 

 water. Loxosoma and PcdiccUina were the first objects investigated, 

 and these animals are not killed by an exposure of as much as half 

 an hour to a 5 i)er cent, solution of potassic nitrate in distilled water. 

 It is tljus (piite easy to free the tissues from the greater i)art of 

 their chlorides by washing with the above-mentioned solution of 

 potassic nitrate ; from this the objects are transferred (naturally with- 

 out the formation of any precipitate) for four or five minutes to a solu- 

 tion of silver nitrate (1/8 to 1 per cent, according to circumstances). 

 After reduction of the silver during exposure to light in the nitrate 

 solution, the tissues may be mounted permanently either in glycerin 

 or in Canada balsam. Very beautiful preparations of Loxosoma were 

 easily obtained by the use of osmic acid aud picro-carmine after treat- 

 ment with silver nitrate. The animal may either be transferred 

 directly from the silver solution to osmic acid (1/2 per cent.) and 

 thence to picro-carmine, reduction taking place during the jirocess, or 

 the osmic acid may be added after the silver has been already reduced 

 in the potassic nitrate. In successful preparations made in the above 

 manner, the limits of all the cells of the ejudermis aud of the alimen- 

 tary canal are exceedingly sharply marked out, the nuclei of these 

 cells as well as of the muscle cells, connective-tissue corpuscles, and 

 other tissue elements, being very distinctly stained. 



Few animals seem to resist the action of potassic nitrate to so 

 great an extent as Loxosoma aud Pedicellina, most forms being either 

 immediately or after a few minutes killed by an immersion in a 

 5 per cent, solution of this substance. Even in many of these cases, 

 the tissues suffer very little histological change, aud can be easily 

 stained by silver nitrate. It is possible that many other salts may be 

 used more advantagetnisly than potassic nitrate in washing the 

 chlorides from the tissues without killing the animal. A 4^ per 

 cent, solution of soJic sulphate may be used instead of the potassic 

 nitrate, over which, however, in most cases it has no obvious advan- 

 tages. 



Balsam of Tolu for Mounting. — Dr. "W. J. Gray informs us that 

 some years ago he tried this substance for mounting, but found that 

 it was open to the great objection of the formation of crystals. Since 

 Mr. C. H. Kain's recommendation of it f he has tried it again, and 

 the slides are already full of crystals. 



* MT. Zool. Stat. Ncapul, v. (ISSi) pp. ii-SG. 

 t See tUia Jourual, iv. (1884) p. 1)^5. 



