COXTKIBUTIOXS TO THE CYTOLLXiY oK THK iJACTElUA. 467 



to the province of morphology, not of chemistry or physics. 

 It is necessary to bear this in mind when discussing it. Hence 

 whether a given body is a nucleus or not can only be decided 

 by studying its morphology and then comparing it with other 

 structures which we agree to call nuclei. Chemical properties 

 and staining reactions may aid us materially in reaching a 

 conclusion, but they cannot alone be used as criteria at 

 present.' If they could, then a pound of nuclear substance — 

 if it could be obtained — would be a nucleus. 



One more point must be mentioned here. It has been 

 many times asserted that Bacteria consist entirely of nucleus, 

 or entirely of cytoplasm — because no cellular differentiation 

 like that of other organisms has been discovered. That 

 Bacteria are composed of cytoplasm is not frequently stated 

 in so many words, but it is often tacitl}'' assumed when speak- 

 ing of these organisms as enucleate. But that Bacteria are 

 nuclei has been definitely stated by many workers — especially 

 in recent years by Riizicka. Now, apart from any work 

 which niay have led to such an interpretation, I should like 

 to point out that such statements are, a priori, nonsense. 

 By " nucleus " and " cytoplasm " are meant definite morpho- 

 logical elements into which most — probably all — cells are 

 differentiated. There is good experimental evidence that 

 neither nucleus nor cytoplasm — specialised parts both of the 

 living protoplasm — is capable of living independently of the 

 other for any length of time. To call a Bacillus a naked 

 nucleus is, therefore, a misapplication of a word in common 

 use. An organism may have a structure similar to that of 

 many nuclei, it may have similar chemical and staining- 

 characters,- but to call it a nucleus in consequence is — far 



^ In connection with the nucleus in Bacteria somewhat similar 

 views have already been expressed by Schaiidinn (1903). It is curious 

 to note how many other writers are so profoundly impressed with the 

 importance of chromatin that they frequently use " chromatin " and 

 •• nucleus "" as though they were synonymous. 



- It shoiild also be emphasised that the "special affinity for chroiiiatin 

 stains," which is often attriljuted to Bacteria, is — as Fischer has 

 pointed out — a myth. 



