362 CHAPTER, XXVII. 



object of study, a thin fixation, one in which the spongioplasm 

 is entirely preserved, but the hyaloplasm only partly, may be 

 the better. 



The spongioplasm is the easier to fix of the two, and the 

 majority of acid fixatives will preserve it more or less ; for 

 instance, the osmic acid, chromic, or picric mixtures, or cor- 

 rosive sublimate. The best images I have obtained are those 

 given by liquid of Flemming or Hermann in cells in which 

 the action of the reagent has been moderate, i. e. insufficient 

 to thoroughly fix the hyaloplasm at the same time. I have 

 also had good results with vom Rath's picro-osmic and picro- 

 platinosmic mixtures, and with acid sublimate. 



Hyaloplasm is not nearly so easy to fix, and there are 

 only two reagents in common use that readily give a really 

 full fixation of it ; these are osmic acid and bichromate of 

 potash . 



Osmic acid acts as a fixative of hyaloplasm in liquid of 

 Flemming or Hermann, but only gives a full fixation in the 

 outer layers of the material ; and in these it easily happens 

 that many or most of the cells are ruined by over-fixation 

 (see 28, 39). 



This defect may be to a certain degree corrected by taking 

 the osmic acid weaker than is usual. Thus by successively 

 reducing the proportion of this ingredient in liquid of 

 Hermann,* I have found that it can be brought down to 

 one eighth of the prescribed amount without loss of the dis- 

 tinctive characters of the fixation. But it cannot be entirely 

 omitted without the character of the fixation changing 

 altogether. 



NIESSING (Arch. f. mik. Anat., xlvi, 1895, p. 147) has the following 

 two modifications of Hermann's mixture : 



(1) Platinic chloride, 10 per cent, solution . . 25 



Osmic acid, 2 per cent 20 



Glacial acetic acid ... 5 



Distilled water . 50 



(2) The same with saturated aqueous solution of corrosive subli- 

 mate instead of the water. 



Tnej are both of them, in my opinion, as ill-imagined as possible. 

 They contain some three times as much platinic chloride as Hermann's ; 

 aii'l Hermann's contains already quite as much as it can bear, and, I think, 

 much more than is advisable : see the proportions in the mixtures 49 

 and 53. RABL (Aiiit. Am., iv, 1889, p. 21) employed it of from ^ to per 

 cent, strength, which seems to me much nearer the mark. 



