510 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tissno yellow and well defined. Animals preserved in spirit may be 

 placed for twelve to eighteen hours in 1 per cent, osmic acid, and after 

 being well washed stained with hematoxylin. 



Preparation of Echinodermata.* — Dr. 0. Hamann preserves the 

 organs of Echinodermata in Flcmming's chromo-osmium acetic acid. 

 For preserving and decalcifying small animals chromic acid was used ; 

 animals preserved in strong spirit were afterwards decalcified by immer- 

 sion in a 0*3 per cent, solution. After having been washed for twelvo 

 hours they wero stained with hematoxylin. For examining the anal 

 blood-lacunee, the sea urchin is well hardened in spirit, the anal parts 

 are decalcified in 1 : 400 chromic acid, and stained with a neutral carmine 

 solution. Decalcification in hydrochloric acid or in chromo-nitric acid 

 is less satisfactory, as the tissues are more affected. The pedicellaria 

 can be cut without being decalcified, and after being carefully washed, 

 stained with carmine or logwood. 



For examining the glandular organ, the so-called heart, treatment 

 with the anilin dyes (safranin, methyl-green, anilin-green) was found to 

 be advantageous. Excellent preparations of organs of Sphser echinus 

 granulans, hardened in a 1/2 per cent, chromic acid, were obtained by 

 staining the sections with Schiefferdecker's anilin-green, absolute alcohol, 

 bergamot oil or xylol, paraffin, xylol, xylol-balsam. The author prefers 

 xylol to turpentine, chloroform, and oil of cloves. 



Methods of Fixing and Preserving Animal Tissues.! — The pre- 

 sent systems of fixation may be resolved, says Dr. N. Kultschizky, 

 into three : — (1) The chromic acid salts of potassium and ammonia and 

 mixtures of those with other salts (Midler's and Erlicki's fluids) fix 

 histological objects well, but this method, according to Prof. Flemming, 

 is not suitable for examining the process of karyokinesis. Prof. Virchow 

 has, however, recently stated that the deficiencies of chromic acid salts 

 may be obviated if they be dissolved in spirit in the dark. (2) The 

 second group of fixatives consists of chromic acid, osmic acid, picric 

 acid, acetic acid, &c, and includes the mixtures of Flemming, Kleinen- 

 berg, Fol, and others. This group, particularly the Flemming's 

 mixture, is especially valuable for demonstrating the division of the 

 nucleus. Chromic acid, it must be remembered, almost always pro- 

 duces an insoluble precipitate of albumen, and consequently is decep- 

 tive, from calling into existence a tissue-like structure and for forming 

 insoluble and impermeable combinations, as, for example, in objects 

 with a muscular tissue. (3) The best fixative of all is alcohol, but, 

 as it has a great attraction for the watery element of albumen, it pro- 

 duces considerable alteration in the form of objects. 



Hence, as none of the three foregoing methods are perfect, tho 

 author has found it advisable to pursue the following course, which in- 

 cludes the least defective points of all three. 



The fixative is prepared by mixing excess of finely powdered bichro- 

 mate of potash and sulphate of copper in weak spirit (50° ), and 

 allowing them to stand in completo darkness for twenty-four hours. 

 A greenish-yellow fluid is hereby obtained, and this, before being used, 

 is acidulated with acetic acid (five or six drops to 100 ccm.). 



The object to be fixed is placed in the fluid prepared as above for twelve 



* Jenaisch. Zeitschr. f. Naturwiss., xxi. (18S7) pp. 87-2GG (13 pis. and 2 figs.). 

 t Zeitschr. f. Wiss. Mikr., iv. (1887) pp. 345-tf. 



