104 THE NATURE OF LIFE 



than inhibit the multipUcation of a vir- 

 ulent strain and allow a less virulent one 

 to develop. 



The case is quite different when a cell 

 takes on new characters as the result of 

 treatment and its descendants retain 

 these characters. In this connection we 

 may mention the remarkable results ob- 

 tained in the artificial production of can- 

 cer. 



Yamagiwa and Ichikawa produced 

 cancer by painting the ears of rabbits with 

 coal tar. They were led to this experi- 

 ment by the well-known fact that chim- 

 ney sweeps and tar workers are partic- 

 ularly subject to cancer. The effect of 

 the tar is to stimulate normal cells into 

 an abnormal growth and multiplication. 

 This continues in the descendants of 

 these cells since they continue to produce 

 cancerous tissue and in the case of white 

 mice Deelman was able to transplant 

 such cancers to a normal animal where 

 the cancer continued to grow. This can- 

 cer was then again transplanted to a nor- 



