330 CYTOLOGICAL METHODS. 



useful for bringing out reticula and nucleoli. Chloride of 

 gold preserves the forms well, but generally leaves the nuclear 

 structures unstained. Nitrate of silver is hopelessly uncon- 

 trollable in its action. Alcohol has much the effect of chromic 

 acid, but often causes a much greater shrinking of the nuclei. 

 Bichromate of potash and chromate of ammonia bring out very 

 sharply the appearance of a reticulum, but these appearances 

 cannot be accepted as true (1. c., p. 334, et seq.). 



" Those who seek to xtudij cdl-dii'ixion by means of bichromate 

 of potash or other chromic salt* arc hopelessly in the wrong 

 road." And this because of the injurious action of the 

 bichromate, not on the body of the cell, which it preserves 

 well, but on the chromatin structures. Chromic salts are 

 excellent reagents for general histological work, but not for 

 nuclear structures. They dissolve nucleoli, destroy nuclear 

 " net works," and swell up and distort karyokinetic figures to 

 such a degree that the appearances obtained from them are 

 merely unnatural caricatures of the true structure. 



Altmann's nitric acid method is excellent for the purpose 

 of hunting for cell- divisions in tissues; but the minute struc- 

 ture of the figures is not so well preserved as it is by means 

 of chromic or picric acid. The same must be said of Kleinen- 

 berg's picro-sulphuric acid method. (I am not alone in hold- 

 ing that this is a most untrustworthy cytological reagent; see, 

 for instance, HOLL [Sitzb. h. Acad. Wiss. Wien, xcix, 1890, 

 p. 311 ; Zeit.f. wiss. Mik., ix, 1, 1892, p. 89], who found that 

 it frequently reduced chromosomes to the state of mere lumps, 

 " Krumeln.") 



There are two fixing mixtures which may be said to be 

 classical for cytological studies, FLEMMING'S chromo-aceto-osmic 

 acid mixture, 35, 36, and HERMANN'S platino-aceto-osmic acid 

 mixture, 51. As to the former of these, Flemming has the 

 following explanations : Attempts to omit the chromic acid 

 from the formula did not give good results. The omission of 

 acetic acid (as in Max Flesch's formula, 34) causes the 

 figures to be far less sharply brought out. The presence of 

 acetic or formic acid in all osmium solutions is favorable to 

 the precision of subsequent staining with ha3matoxylin, picro- 

 carmine, or gentian- violet. But mixtures of osmic and acetic 

 acid without chromic acid (Eimer) do not give such good 

 results as the chromo-aceto-osmic acid mixture. Mixtures 



