THE CKLL MKMJJUANK. 149 



j)u.sitii)u of this iisli is still unknown. Moreover, we have ulwi 

 to reckon with tlie still uninvestipite«l puKsihility that the ash 

 itself is introilueed into the meml>i-ane <liiring the pioceiis of 

 extraction. As rej»artls the iiUiount of nitio;»en in the luem- 

 biiine, one is unahle to tintl similar un:iniinity in the re|K»rt8 

 of the tlilTi'icnt woikeis, fur whereas ScilLossUKKiiKK (1.) could 

 not reduce it helow 0.5 per cent, and E. S.\lkowski (VI.) 

 ai'rived at ahout the s;inie limit (0.4 to 0.5 per cent.), both 

 MiLDKK, and also N.KGELi and LoEW (II.) claimed to have 

 eliminated it to a tnice, thou^jh hy the use of re;igent,s {e.</. 

 Strong, warm hydrochhiric acid) which few substiinces could 

 withstand undecomiK)se<l. 



!$ 250. The Cell Nucleus. 



Only in comparatively rare instiinces is the cell nucleus easily 

 reco^jnisjible in tlie living cell without some preliminary treat- 

 ment, its refractive power l»eing usually only a little greater 

 than that of the cytoplasm. In years gone by, when the 

 opticjil instruments available were inferior in power to those 

 of the present day, the nucleus thus escaped the ob.servation of 

 even practised microscdpists Whereas Xa'geli, as long ago 

 as 1S44, fre(p»ently reniaiked in the cells t)f wine and beer 

 yeasts "a small nucleus of whitish mucus adjoining the nieni- 

 brane," the presence of which was confirmed liy M. J. S< iii.KlitEN 

 (I.) in 1841;, EuxsT 1{hle<kk (I.) on the Dther hand a.sserted in 

 1861 that he had never siieceedetl in finding the same. The 

 earliest inipoitiint advance was made towards the close of the 

 eighties, b\ the application, U) the In^tjinical examination of cell.s, 

 of the micriH-liemical staining proces.ses already .succe.ssfully 

 use<l in the domain of zoology. Fii. ScuMlTZ(I.) in 1879 pre- 

 pared yeast cells by hanlening them in a .s;itunited .solution of 

 picric acid, then washed them with care, and stiined them by 

 immer.sion in hiematoxylin, followed l»y repejite<l washing. In 

 this way he succeeded in discovering in each cell a small 

 blue-stained bodv, which was clearly distinguishable from the 

 surrounding colourless plasma, and, both in this and .several 

 other re.spect-s, behaved very like the nucleus of the animal cell. 

 Stiasbtuger, in repeating the tests several yeais latt«r, tlesc,inttHl 

 on the somewhat ditlicult performance of this staining jiri>cess, 

 and it is therefore not surprising that other experimenters 

 of both sexes, »•.«/. Kit. Kit.xssxEit (I.) in 1S85, and Siuo.via 

 KiSKXScniTZ ( 1.) ten ye.irs lati'r. tried it without success. No 

 more fortunate in this respect was .Ion. K.\r.\i (11.) who. in 

 1S90, on the Ivisis of his staining te.sts (mentione<l in later 

 p;u*agraplis) expres.sed the opinion that the cells of yeast are 

 non-nudoated. A similar negative .-t.indpoint seems to have 



