AMITOSIS IN CELLS GROWING 'IN VITRO. 



C. C. MACKLIN. 



(From the Department of Anatomy, Johns Hopkins University, and the Marine 

 Biological Laboratory, Woods Hole, Mass.) 



(3 PLATES, 27 FIGURES.) 



CONTENTS 



Introduction 445 



Method 446 



Observations 448 



Nuclear division by amitosis 449 



Subsequent history of cell containing a directly divided nucleus 453 



Discussion 455 



Fragmentation 458 



Vital stains 458 



Summary 459 



Literature cited 460 



Explanation of Plates 462 



INTRODUCTION. 



During recent years the conviction among cytologists has 

 become more and more strongly intrenched that the problem of 

 amitosis can not be satisfactorily solved by investigations based 

 alone upon the study of non-living tissue, but that its successful 

 conquest must rely principally upon the correct interpretation 

 of the succession of morphological and physiological changes 

 revealed by prolonged observation of the living cell, under normal 

 and artificially varied conditions. Yet until the advent of the 

 tissue culture method, workers in biology might well have de- 

 spaired of ever being able to attack the question in this way. 

 It is fortunate, therefore, that the technique of tissue cultivation 

 has been so perfected that even the minute structural details 

 of the living cell may be readily observed, and that the inspection 

 may be continued for hours at a time; fortunate, too, that con- 

 figurations which may be interpreted as stages in the process of 

 direct division, such as dumb-bell-shaped nuclei apparently 

 undergoing constriction, and bipartite nuclei, are not infrequently 

 found in tissue cultures, and, furthermore, that fixed and stained 

 preparations, to assist in the interpretation of the appearances 



445 



