1C)« 



Till' cullurps used in all the oxporinients were derived 

 from a *.• inonllis old strain of chicken fihi-ohlasls. The strain 

 was isolali'd and culli\ alcil in llu- I n s I i I n I c of < 1 c ii c r a 1 

 Palholo^N of llu- l'nivcrsit> of ('. o p c n h a <f c n. 



The preliminary experiments were briefly made in the 

 following way. Single, good cultures of fibroblasts were cut 

 into [—(• pieces of equal size and each of the pieces kept 

 as individual cultures under identical conditions for 21 hours. 

 ^^'ith various intervals (from half an hour to four hours; 

 two cultures, derived from the same culture, wei'e fixed 

 and stained simultaneously. Two cultures were fixed simul- 

 taneously to let them control one another. — In these 

 stained specimen, the cells in any stages of division were 

 counted in the line of peripher3% and after that all the 

 tissue cells in the line of periphery and the percentage of 

 cells in a stage of division w'ere figured out. The line of 

 periphery of the growing piece of tissue is a rather definite 

 thing. As peripherial cells only those were considered w^hich 

 were outermost, i. e. cells with the one end in contact with 

 another cell and the other end free. 



The few experiments of this kind gave only a weak con- 

 firmation of the earlier observations which should indicate 

 that the percentage of dividing cells differ from time to 

 time. The two cultures taken out and fixed simultaneously 

 proved to have a jiercentage of dividing cells very much 

 alike within the accuracy of tiie e\j)eriments. 



The result of one of these jjreliminarv experiments can 

 be seen in the table 12. The average percentage of mitotic 

 cell divisions going on at a given moment undei' the ex])eri- 

 mental conditions was found to be about 2 per cent. The 

 figures for the percentage of the two or three cultures fixed 

 at the same moment are not so absolutely bad. The ex- 

 periments gave only a rather weak indication that there, 

 at a certain moment, are many cells dividing and at other 

 times relatively few. 



