BINUCLEATE CELLS IN TISSUE CULTIKES. 95 



Altogether the various forms of the nucleus in which spiremes are found in 

 tissue-culture prei^arations resemble strikingly the findings of Karpow in the leuco- 

 cytes of urodele amphibia. This similarity is brought out in the following paragraph 

 from Maximow (1908, p. 95): 



"Nun ist es aber nach Karpows Untersuchungen ziemlich sicher, dass hier die Kerna- 

 mitose zwar zur Kernpolymorphie und sogar zu sicherer Kernteilung fuhrt, dass sie aber 

 doch keine richtige Zellvcnnehrung nach sich zieht. Wenn die Leukocyten mit amitotisch 

 zerschniirtem Kern sich teilen , so geschieht dies eben auf dem Wege der Karj-okinese, und 

 aus einem zerschniirten Kern oder sogar aus mehreren einzelnen, ganz getrennten, durch 

 Amitose erzeugten Kernen entsteht dann eine einzige, gewohnlich regehnassige, mitotische 

 Figur. Man findet Spii'cino in ring-, hantel-, rosenkranzfoi'inigen Kernon, oft auch zwei 

 oder mehrere einzelne Kerne in einer Zelle, alle gleichzeitig ini Zustande des Spirems, woraus 

 dann immer ein gewohnhcher ]\Iutterstern resultiert." 



Maximow also shows a spireme in a dumb-bell-shaped nucleus found in his own 

 material, and observes: 



"Die tief eingeschniirten, oder auch seiion ganz zerteiUen Kerne konnen in Mitose 

 treten und man bekommt dann hantelforniige Spireme (fig. 7) oder zwei kugeUge Spireme 

 nebeneinander in ein und derselben Zelle (fig. 8)." 



Thus it would seem that the nucleus enters upon the process of mitosis when- 

 ever the stimulus initiating this process occurs, whether rounded, bent, undergoing 

 constriction, or divided into two parts, and in all of these, after the single spireme 

 has been formed, the process is apparently identical. 



The question as to whether or not the cytoplasm of the cell divides following 

 direct fission of the nucleus, to form two separate and distinct cells, has been much 

 discussed by vai'ious authors, among them Maximow (^1908), who found — besides the 

 cases in which the amitotically divided nuclear portions formed a single combined 

 mitotic figure and divided by karyokinesis— also instances where such portions simply 

 became separated from one another and surrounded by protojilasm, to form ordinary 

 mononucleate cells. In short, ^laximow believes that, though amitosis of the 

 nucleus may be followed by cell division arising through a process of mitosis involving 

 the directly divided nuclear fragments, yet it can lead directly to cell proliferation 

 without intervening mitosis. As such a method of actual cell multiplication, 

 Maximow believes that amitosis functions in certain areas of the normal develo))ing 

 tissue of the rabbit,, and he has found it also in the guinea pig. Furthermore, he 

 expresses the view that cells arising by direct division can later divide by mitosis, 

 but his reasons for the latter assumption are not given. 



On the other hand ther(> are those who oppose this view and believe that nuclear 

 amitosis is never followed by cell amitosis. P\)r instance, Karpow ( 1904), according 

 to Maximow (1908, p. 89) came to the conclusion, based upon his observations 

 upon the leucocytes of urodele amphibia: "dass in den P'allen, wo richtige Amitose 

 wirklich vorliegt, man eigentlich doch nur Kernvermehrung annehm(>n kann, keine 

 Zellvermehrung." This view is in agreement with the findings of ("onklin (1903. 

 p. 671) for follicular ei)ithelial cells of the common cricket. 



No reliable evidence that fission of the cytoplasm follows that of the nucleus 

 has been found in the tissue cultures examined by me. It is cjuite true that so-called 

 "paired" cells ((' c, cells closely resembling one another in form, staining, etc., 



