COMl'OSHT/OX OF MCLEI 45 



•<ils(» no polassiuin,-' hut tlic ehromatiii coiitaiiis lii-iiily lioiind ii-oii. 



Nucleoli, wiiicli not all x'ai'iotios of iiudri |)oss('ss, diU'ci- i'fom Ihe 

 otluu' imeli'ar .sti'ucturrs in liavin*^' an at'finily for acid rallicr tlian for 

 basic dyes,-"* at least in fixed tissues. Their clieinical composition has 

 not been ascertained. Zacliarias considers the nucleoli as composed 

 of nuclein well saturated with protein, because of its staining re- 

 actions and its relative insolubility in alkalies, and classes it with 

 j)lastin or linin, which forms the achromatic part of the nucleus and is 

 also present in the cytoplasm. jMacallum -° found that they reacted 

 for organic phosphorus microchemically, but less strongly than did 

 chromatin fibers. 



The nuclear membrane is an uncertain structure, at times dense 

 and staining as if formed of a layer of chromatin, in other cells stain- 

 ing like the cytoplasm with which it seems to be continuous, in most 

 cells disappearing during karyokinesis, and in some protozoa being 

 entirely absent. Naturally the composition of the nuclear membrane 

 is unknown, l)ut it is probable that it acts as a diffusion membrane of 

 partially seaiii^ermeable character, maintaining different conditions 

 in nucleus and cytoplasm. 



Functionally the nucleus is the essential element of the cell ; an iso- 

 lated nucleus with but a minimum of cytoplasm may be able to de- 

 velop new c3'toplasm. Init isolated cytoplasm soon disintegrates, al- 

 though it may manifest life for some time by movement and chemical 

 activities. A popular theory is that synthetic, constructive processes 

 occur in the nucleus or under the influence of its products, but to 

 what the nucleus owes these hypothetical powers is unexplained. 

 More tangible are the theories based upon the work of Spitzer, Loeb,^° 

 Lillie "^ and others which suggest that the oxidative processes of the 

 cell depend upon the nucleus, hence portions of the cell cut away from 

 the nucleus undergo asphyxiation. As Loeb-says, "By cellular struc- 

 ture we understand the fact that there must be a definite maxinml dis- 

 tance between the elements of the protoplasm and the nearest nu- 

 cleus. ' ' However, more recent work casts doubt on the dependence of 

 oxidation on the nucleus.'^" 



It should be mentioned that certain cells, such as bacteria and algfe, 

 seem to have no true nuclei, but IMacallum ''- found that the forms he 

 examined gave reactions for phosphorus and iron in a similar way 

 to the nucleojiroteins of a nucleus, suggesting that in such cells the 

 nuclear elements are diffused through the cell rather than differen- 

 tiated. To quote Wilson: "The term 'nucleus' and 'cell body' 



27 .Jour, of Physiol., 1!)05 (32), 95. 



28 Xvicleoli of nerve-cells are an exception, beinfr basophilic. 

 20Proc. of the Royal Society, 1S98 (6.3), M'u . 



30 "Studies in General Physiolntjy," Chicago. 190.5. 



31 American .Journal of Plivsiolopv, 1902 (7), 412. 

 siaSee Lillie, Jour. Biol. Ciieni., 1913 (15), 237. 



32 "Studies from the University of Toronto," 1900. 



