190 Eisen: Notes on fixation, stains, tlie alcohol niethod, etc. XIV, 2. 



qualities of the metal. To begin with, I used a mixture of platinum 

 chloride with iridiurn chloride in */ 2 per cent. Solutions : 



Platinum chloride, 1 /. 2 per cent. ... 50 pts. 



Iridium chloride, 1 / 2 per cent 50 „ 



Glacial acetic acid 1 pt. 



This fixed the testes of Dieniyctylus torosus, our common Salaman- 

 der, in a very satisfactory way. The spindles, chromosomes, and 

 archoplasm left nothing - to be wished for; the absence of the osmic 

 blackening being especially desirable. But this mixture, like all 

 other fixatives , possesses the undesirable quality of either over- or 

 underfixing the three outermost cell-zones in the testes. Hermann's, 

 Flemming's, and other fixatives containing osmic acid are even worse 

 in this respect , sometimes ruining six or more of the outer nuclei 

 all around the edge. I soon found that by simply using iridiurn 

 chloride and acetic acid I could fix the testes with facility in such 

 a manner that there would be no difference between the inner and 

 outer nuclei, and that even the outermost nuclei would show their 

 spindles, chromosomes, and archoplasm in a most satisfactory manner. 

 Both the resting and dividing cells are eqiially well fixed. For staining, 

 any of the aniline colors may be used, such as Flemming's triple 

 stain , eosin-toluidine , congo-red-toluidine , Bordeaux-red-thionin , and 

 many other combinations. Among the most satisfactory stains, how- 

 ever , were the iron - ha3matoxylin and the ruthenium - red - thionin 

 combinations. The liquor ferri sulfurici oxydati is much to be 

 preferred to any other iron Compound, as it leaves no deposit nor 

 precipitate. At present I use the iridiurn chloride in two different 

 Solutions : 



I. Iridium chloride, 1 / 2 per cent. . . . 

 Glacial acetic acid 



II. Iridium chloride, 1 j 5 per cent. . . . 

 Glacial acetic acid 



The testes are fixed in six hours or less, but I have at times left 

 them in the fixative for 12 or even 24 hours, and I suppose that 

 immersion even for months would not be injurious, or might even 

 improve the tissue. The tissue does not become brittle, but, after 

 passing through the regulär process of embedding, sections up even 

 better than tissues fixed with any of the osmic acid combinations. 

 A few hours in distilled water washes out all the fixative, and 

 the testes , which are at first brownish , turn white , even after one 



