148 SUMMARY OF CURRENT RESEARCHES RELATING TO 



washing away the osiiiic acid, place the objectH iu a very dilute solution 

 of potassic acetate iu au ojjcu vessel, and leave them for two or three 

 days, during which much of the solution evaporates. Finally, transfer 

 to a saturated solution in order to clarify so far as possible. Very 

 beautiful preparations are said to be thus obtained. 



The course of the nerves may be easily traced in specimens that 

 have lain several days in 1 per cent, formic acid. The tissues swell 

 up strongly and become quite transparent, so that tlie nerves can 

 be seen. If the muscular layers be separated from the subcuticula 

 in specimens thus treated, and then stained in gold chloride, the 

 lateral nerve-trunks may be clearly shown. For the histological 

 study of the nerves, the Echhiorhjnchi should be treated with chromic 

 acid and then stained deeply with borax-carmine. 



Chromic acid preparations are also best for the study of the subcu- 

 ticula. Echinorhynchi live for days in a 0*1 per cent, solution of 

 chromic acid, but eventually die in a fully extended condition. Such 

 preparations, after treatment with alcohol, may be coloured at once ; 

 or, after washing a day or more in running water, exposed to the action 

 of osmic acid, and then coloured in borax-carmine. 



For the study of the sexual organs, a very dilute picro-sulphuric 

 carmine, which according to Saflftigcn is the best staining fluid, must 

 be allowed to act a long time (often one or more days) ; after a deep 

 stain has been taken the prejiaration should be partially discoloured 

 by the use of hydrochloric acid in the ordinary way.* 



Action of Light on Objects hardened in Chromic Acid.f — Dr. H. 

 Virchow shows that in tissues hardened in chromic acid, if subsequently 

 placed in alcohol, a precipitation takes place, in the presence of light, 

 of destructive secondary products of chemico-physical action. Part of 

 the tissues is dissolved and thrown down as a fine brown granulation. 

 In the dark, this result is avoided, as also when the tissue is first 

 dehydrated before placing it in (absolute) alcohol in the presence of 

 light. 



Haacke's Dehydrating Apparatus.^ — Dr. W. Haacke has devised 

 the apparatus shown in fig. 27 for dehydrating objects so as to avoid 

 tlie tedious process of placing them first in weak and afterwards in 

 stronger and stronger alcohol. 



It consists of a glass vessel 50 cm. high and 25 cm. in diameter, 

 with a tap at the bottom and a top fitting air-tight, having one 

 central and eight (smaller) peripheral apertures. These are closed 

 by the tubes shown in the figure, also fitting air-tight (but easily 

 removable), the lower end being drawn into a capillary point and the 

 upper widened out to 5 cm. in diameter, and having a closely-fitting 

 glass stopper. The tubes extend 25 cm. into the glass vessel and 

 stand up 10 cm. above it. They should be thick and have a lumen 

 of at least 1/2 cm. The central one should hold 100 c.cm. and the 



• See Amer. Naturalist, xviii. (1884) p. 1291. 

 t Arch. f. Mikr. Anat., xxiv. (1884) pp. 117-19. 

 X Zool. Anzeig., vii. (1884) pp. 252-U (1 fig.). 



