838 



THE CARCINOGENIC STIMULUS 



Fig. 29. Thymic lymphosarcoma (thymoma "th") development in a mouse injected with 

 estrogenic hormone. Depending upon genetic constitution, similar neoplasms may be 

 induced by carcinogenic hydrocarbons, X-rays or certain chemicals {e.g. urethane, 

 thiotepa), either independently or in conjunction with other agents. 



Fig. 30. Mouse with hepatoma (h) and hemangiomas (ha) of the liver. Hepatoma occurs 

 more frequently in male than female mice, and the incidence in the sexes can be altered 

 by administration of sex steroids. 



Legends continued on p. Ssg 



