80 BINUCLEATE CELLS IN TISSUE CULTURES. 



Harrison (1913, p. 67) has shown that the behavior of cells growing in culture 

 media is comparable to that of cells growing in the embryonic body, and it is 

 reasonalile to assume that the beliavior of these binueleate cells in tissue cultures 

 a])pr()ximates the beliavior of similar cells in the developing embryo. Hence the 

 vital i^henomena manifested liy such binueleate cells in tissue cultures afford n^liable 

 evidence as to the changes which take place in similar cells livhig under normal 

 conditions in the corresponding embryo. 



ORIGIN. 



If we inquire as to the origin of these binueleate cells of (lie new growth we are 

 confronted with four possibiliti(>s, viz: 



(a) Migi'idioii as a binueleate coll from the oxplanted tissue. 



(b) Fusion of the cytoi)lasni of two previously separate cells without fusion of the 



nuclei. 



(c) Division of the nucleus by mitosis without division of the cytoplasm. 



(d) Division of the nucleus hy amitosis witliout division of the cytoplasm. 



This list does not include the theoretical origin of nuclei de novo from the cyto- 

 plasm, or their development from extruded chromidial substance (Young, 1913). 

 These hypotheses do not app(>ar to have been substantiated, and no evidence in 

 favor of either appears in tissue-culture jM-eparations. 



First, considering (a), we fintl that twin nuclei occur in the area of new growth 

 immediately surrounding the original tissue, and such forms are well known in 

 embryonic tissue. Thus it is i)rol)able that many of the binueleate cells in the new 

 growth have migrated as such from the explanted tissue. The great increase in 

 l)r()])ortion of double-nucleated cells in the second 24 hoiu's, however, as has been 

 noted, suggests that not all of these cells are of migratory origin, but that some 

 have probably arisen in the new growth itself. This view is borne out by observa- 

 tions upon the living cell, as will be shown, where a single nucleus has been seen 

 to become divided directly- into two parts, and also by the finding of nuclei in the 

 act of direct division in the fixed preparations. 



The binueleate cells which have migrated as such from the original piece have 

 probably originated therein in the same manner as those arising in the new growth. 

 Giant cells can hardly be considered to have migrated as such from the original 

 piece, for in the zone immediately surrounding the latter they are not found. 



Regarding {!>) , it may be said that no ajipearances which could be interpreted as 

 transitional forms have been found in fixed and stained preparations or in cultures 

 vitally stained, neither has the process been observed in the living culture. I 

 therefore regard it as an im]irobable hypothesis. This could hardly be considered 

 as an explanation of the formation of giant cells, for that would postulate the 

 fusion of a multitude of previously separate cells, of which there is no evidence in 

 the material examined. 



It may be noted that Lambert (1912?>), who brought about the formation of 

 giant cells by fusion of monomiclear cells in cultures from chick spleen, failed to get 

 such cells in cultures from chick heart. Furthermore, Lambert (1912a) recognized 

 three other types of giant cells in ti.ssue cultures, besides this. 



