852 



THE CARCINOGENIC STIMULUS 



II 



Fig. 37. Mammary cancers (m) occurring following the feeding of methylcholanthrene 

 to a mouse which did not possess the mammary tumor agent. The agent has not been 

 demonstrated in such tumors by bioassay. 



Fig. 38. Mouse lung with a primary lung tumor (alveolar adenoma "as"). At (b) are metas- 

 tases of a mammary cancer within blood vessels. Pulmonary alveolar adenomas of mice 

 may be induced by carcinogenic hydrocarbons, urethane or nitrogen mustard, response 

 being determined by genetic constitution. X go 



Fig. 39. Whole mount of the skin with mammary glands (mg) attached, to demonstrate the 

 development of multiple mammary cancers (mc) in a mouse fed methylcholanthrene. This 

 animal did not have demonstrable mammary tumor agent. 



Fig. 40. Portion of a stained dissected mammary gland to demonstrate hyperplastic nodules 

 (n) on the mammary tree of a high cancer strain female. These nodules are pre-cancerous 

 lesions. Multiple nodules occur on the mammary tree of mice fed methylcholanthrene, but 

 these nodules differ histologically from those occurring spontaneously. X 2 



Legends continued on p. 853 



