CHAPTER XXVI. 301 



clxxx, 1905, p. 363 ; MACALLUM, Ergeb. Phys. Wiesbaden, vii, 1908, 

 p. 612. 



For Potassium see MACALLUM, Journ. Phys. Cambridge, xxxii, 1905, 

 p. 95 ; Ergeb. Phys. Wiesbaden, vii, 1908, p. 600. 



For Guanin see GIACOMO, Zeit. wiss. Mik., xxvii, 1910, p. 257. 



Concerning the microchemistry of the cell in general, see further fourth 

 edition; also CARNOY and LEBRUN, La Cellule, xii, 2, 1897, p. 194.; 

 ZIMMERMANN, Die Morphologic u. Physiologic des Pflanzlichen Zellkernes, 

 Jena, 1896 (treats also of the animal cell) ; HAECKER, Praxis u. Theorie 

 der Zellenund Befruchtungslehre, Jena ; PRENANT, Journ. Anat. Phys., 

 xlvi, 1910, p. 343. 



651. Cytological Fixing Agents. A fixing agent that is good for 

 one element of a cell is not necessarily good for all others. As 

 regards the nucleus, all fixatives should be acid ; for if not they will 

 not satisfactorily preserve either chromatin or nucleoli. For 

 instance, bichromate of potash, if not rendered acid, fixes chromo- 

 somes and nucleoli in a distended state so that clear images of them 

 are not obtained. Acids contract them somewhat, and so give 

 them sharper outlines. The fixatives mostly employed for nuclei 

 are liquid of FLEMMING and liquid of HERMANN. There is a slight 

 difference between them. Liquid of Hermann, owing to the platinum 

 chloride, causes chromatin to shrink more than liquid of Flemming 

 does, and for this reason is supposed to give clearer images of 

 chromosomes, especially of their splitting. I find that it generally 

 makes them shrink too much, and that it is not at all good for spindles. 



For many, if not most objects, I prefer to these two reagents 

 BOUIN'S picro-formol, which gives a highly faithful preservation 

 and a more penetrating and equable fixation. 



For spindles I recommend Flemming (picro-formol does not give 

 quite such bold images). 



Some of the finest chromosomes I have seen have been fixed with 

 LINDSAY JOHNSON'S mixture ( 44), and liquid of TELLYESNICZKY 

 has given me others nearly if not quite as good. 



As regards the cytoplasm. Cytoplasm is made up of two elements : 

 a fibrillar element the spongioplasm or mitome ; and a more or 

 less granular liquid that bathes it the hyaloplasm or enchylema. 

 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 " pre- 

 cipitation forms," see 29), and the secretions or other enclosures 

 that may be present in it, may so mask the fibrils of tlie spongio- 



