CONDITIONS OF CELLULAR IMMORTALITY 61 

 system, the heart, and mesenchymatous tissue of the 

 chick embryo. At the same time Carrel was carrying 

 on studies in this same direction at the Rockefeller In- 

 stitute. In his laboratory were made the first successful 

 cultures in vitro pf the adult tissues of mammals. He 

 developed a method of culture on a plate which permitted 

 the growing of large quantities of material. He found 

 that almost all the adult and embryonic tissues of dog, 

 cat, chicken, rat, guinea pig, and man could be cultivated 

 in vitro. Figure 15 shqws a culture of human tissue, 

 made at the Rockefeller Institute. I am indebted to 

 Doctor Carrel and Doctor Ebeling for permission to pre- 

 sent this photograph here. 



According to the nature of the tissues cultivated, con- 

 nective or epithelial cells were generated, which grew out 

 into the plasma medium in continuous layers or radiating 

 chains. Not only could normal tissues be cultivated but 

 also the cells of pathological growths (cancer' cells). 

 It has been repeatedly demonstrated that normal cell 

 division takes place in these tissues cultivated outside the 

 body. The complex process of cell division, which is 

 technically called mitosis, has been rightly regarded as 

 one of the most characteristic, because complicated and 

 unique, phenomena of normal life processes. Yet this 

 process occurs with perfect normality in cells cultivated 

 outside the body. Tissues from various organs of the 

 body have been successfully cultivated,; including the 

 kidney, the spleen, the thyroid gland, etc. Burrows was 

 even able to demonstrate that the isolated heart muscle 

 cells of the chick embryo can divide as well as differen- 

 tiate, and beat rhythmically in the culture medium. 



Perhaps even more remarkable than the occurrence 

 of such physiological activity as that of the heart muscle 



