167 



A favourable mclhod for isolalin^f tissue cells and laler 

 embedding Ihern in a suitable fixed medium, has been worked 

 out, and slill it has not l)een i)ossible lo observe cell division 

 when the cells were isolated. Multiplication look 

 place only in those cases where several i n- 

 d i V 1 d u a 1 s were in close contact w i t h e a c h 

 other. 



A furthei slufly has also i)een undertaken to determine 

 the vitality and ability to proliferation of the different parts 

 of the tissue cultures. It was ascertained that when these 

 parts contain few or scattered cells, no growth took place, 

 but when the parts contained cells in close contact with one 

 another, growth took place after the parts had been trans- 

 ferred into a new' medium. The healthy condition and the 

 signs of permanent life in these isolated cells, seem to 

 point to the urgent necessity for direct contact in pro- 

 ducing multiplication. However, other explanations of this 

 phenomenon have been discussed. The direct protoplasmic 

 connections, which are always found in the well-growai cul- 

 tures, and the cytotropic character of the tissue cells, 

 speaks directly in favour of the assumption, that the cells 

 are individually dependant on one another. 



In order to go deeper into the problem and endeavour 

 to prove the suggestion, that divisions of cells take place 

 only when several tissue cells are present and in good proto- 

 plasmic contact, it was imjiortant to know a little about the 

 number and ])ercentage of cells undergoing divisions at a 

 given moment in vitro, and to locate these dividing cells 

 in relation to cells which have divided previously. 



To attack the problem different methods were devised. 

 Some preliminary experiments were undertaken. Several 

 times I have been struck by the fact, that some specimen 

 of cultures contained many mitotic figures and at other 

 times specimens were found to contain very few, or at 

 least it was difficult to find any. I have noticed great dif- 

 ference in the numbers of mitosis in cultures of fibroblasts 

 as well as in cultures of epithelium and cartilage. 



