322 m.M'TKu, xxvr. 



and a more or less granular liquid that bathes it the 

 hyaloplasm or onchylema. It does not follow that a 

 reagent that will fix one of these will also fix the other. 

 Nor is it always desirable that both should be equally 

 fixed. 



If you fix both, you will have a full fixation ; but in that 

 case the granules of the hyaloplasm (be they vital, or be they 

 only "precipitation forms/' see 29), and the secretions or 

 other enclosures that may be present in it, may so mask the 

 fibrils of the spongioplasm as to interfere with the observa- 

 tion of it. So that if the latter is the principal object of 

 study, a tJiin 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. 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. Nearly, if not quite, 

 as good, is Bouin's picro-formol, which has the great advan- 

 tage of being very favourable for plasma-staining. I have 

 also had very 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&ndbichromatc of potatfh. 

 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 35). 



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 

 * NIESSINQ (Arch. mik. Anat., xlvi, 1895, p. 147) has the following 

 two modifications of Hermann's mixture : 



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

 Osmic acid, 2 per cent. . . 20 



Glacial acetic acid ...... 5 



Distilled water . ..... 50' 



