256 



and the dead muscular proloplasm. Only leucocytes were 

 found to be able to build uj) their own proloplasm and 

 Iransiorm the serum consliluenls to material which can 

 serve as a food for fibroblasts. I'ibroblasts, epithelial cells 

 and cartilage are not able to live and multiply in media 

 which do not contain embryonic tissue juice. In other 

 words this means that there is a capital difference between 

 the character of normal tissue cells and the Rous chicken 

 sarcoma cells as types of the malignant cells. This fact 

 helj)s us to understand a good deal more of the nature of 

 the malignancy of the sarcoma cells. 



Besides this character, the sarconui cells have a remark- 

 able ability of liquefying the plasma medium, a characteristic 

 which has already been described long ago, and found by 

 almost every investigator who has cultivated malignant tissue 

 cells in vitro. 



To these two biological characteristics of the malignant 

 cells, we may add a third, which, I believe, is at least 

 equally as im])ortant as tiie others. By this it is possible 

 also to explain the propagative and destructive nature of 

 the tumor cells. The sarcoma cells of the Rous 

 chicken sarcoma are observed to divide e ^• e n 

 when the cells are scattered, isolated and in 

 no protoplasmic contact with other cells. 

 In a former chapter: "The integi'ity of tissue cells", it was 

 descril)e(l that normal fibroblasts were not able to divide 

 and multiply from one single cell. Only when several indi- 

 vidual tissue cells were in close contact with one another, an 

 outgrowth of new cells would take place. It was also men- 

 tioned that the colonising abilit}' of normal tissue cells 

 could not only be observed physiologically, but also histo- 

 logically Cultures of normal ril)roblasts, especially after 

 they have been stained and prepared with chloride of gold, 

 show that all cell individuals are in anastomotic connection 

 with one another. The tissue colony, taken as a whole 

 resembles that of a syncytium, more than anything else. 



