A COMPARISON OF MITOSIS IN CHICK TISSUE 

 CULTURES AND IN SECTIONED EMBRYOS. 



ROBERT T. HANCE. 

 NATIONAL RESEARCH FELLOW, UNIVERSITY OF PENNSYLVANIA. 



Those accustomed to working with tissue cultures are, I am 

 sure, seldom troubled with doubts as to the essential normality 

 of the processes going on in these isolated bits of tissue. Others, 

 less familiar with the results and conditions of this type of work, 

 usually make cautious reservations and distinctions in discussing 

 phenomena occurring in living substance under its usual associ- 

 ations and when subjected to the technique of the tissue culture. 

 Through the interest and courtesy of Mrs. M. R. Lewis of the 

 Dept. of Embryology, Carnegie Inst. of Washington it has been 

 possible for me to study mitosis in a number of beautifully fixed 

 preparations of cultures of chick tissues. As this led later to 

 an examination of this process in chick embryos a comparison was 

 inevitable and a note concerning the characteristics of dividing 

 cells as found in tissues existing under the two environments 

 seemed desirable. 



As regards fixation the tissue culture is infinitely easier to kill 

 satisfactorily than a larger mass of tissue. The cells in the 

 culture grow out over the cover glass usually in a single layer and 

 the fixing reagent can come in contact with each cell individually 

 and at once. This is, of course, an ideal which can never be 

 approximated in material that must be sectioned. Consequently 

 many fixatives which give excellent results with cultures are 

 worthless when used on bulkier masses of cells. The size of the 

 cells in the culture is another item in their favor for with the 

 release from the crowded quarters of their usual surroundings 

 they spread over the cover glass and press very closely to it, 

 causing the diameter of the cell to increase greatly, associated 

 with a marked thinning in the plane perpendicular to the cover 

 glass. The cell becomes consequently much easier to see through 

 and its various parts appears spread out in diagrammatic fashion. 



