OYTOLOGICAL MimiODS. 321 



Tor Potassium see Macalltjm, Joiirn. Phys. Cavibridge, xxxii, 1905, 

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



Tor Giianin see Giacomo, Zeit. wiss. Mile, xxvii, 1910, p. 257. 



Ooncerning the microcliemistry of the cell in general see iurfher fourth 

 edition; also Caenot & Lebrun, La Cellule, xii, 2, 1897, p. 194; Zimmer- 

 MANN, Die Morphologie u. Pliysiologie des PflanzUchen Zellkernes, Jena, 

 1896 (treats also of the animal cell) ; Haecker, Praxis u. Theorie der 

 Zellemind Befnichtungslehre, Jena; Peenant, Jamn. Anat. Phys., 

 xlvi, 1910, p. 343. 



647. 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 chromosomes 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 differ- 

 ence 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 make sthem 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 preserva- 

 tion and a more penetrating and equable fixation. 



Alongside of this I would place Cahnoy & Leueun's acetic- 

 acid-sublimate flaid, which gives equally fine images of 

 chromosomes, and is still more penetrating. It is, however, 

 not so good for spindles. For these 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 

 TELiiYESNiczKY has given me others nearly if not quite as 

 good. 



As regards the cyloplasm. Cytoplasm is made up of two 

 elements : a fibrillar element — the spongioplasm or mitome ; 



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