SUSCEPTIBILITY TO TRANSPLANTABLE TUMORS 75 



that the tumor mass under consideration was at the outset a 

 'mixed' tumor, each element being derived from its embryonic 

 anlage (carcinoma from epitheUal cells and sarcoma from the 

 connective tissue). Assuming that connective-tissue products 

 can only be produced by connective-tissue elements, we may 

 conclude that if a tumor mass contained these specialized 

 products it must have also contained functioning connective- 

 tissue elements. Some evidence of this nature has been dis- 

 covered by Haaland, Slye, Holmes, Wells, and Woglom. Haal- 

 and found that in a mixed carcinosarcoma, there were inter- and 

 intracellular fibrils present in the sarcomatous parts. 



B}^ the discovery that myxomatous changes may occur in the 

 connective-tissue part of a carcinosarcoma, Slye, Holmes, and 

 Wells indicated that the sarcomatous part must have arisen in 

 the stroma. Woglom in a recent communication concludes 

 that, since cartilage is found in a carcinosarcoma of the mouse, 

 the sarcomatous element of the mass must have been derived 

 from preexisting connective tissue. 



II. EXPERIMENTAL 



1. Materials 



In order to test how far the conflicting results that have been 

 obtained in investigations with transplantable tumors on the 

 lower animals have been due to the use of various market stocks, 

 careful attention has been given to the strain of mice employed. 



Rigorous inbreeding may or may not produce harmful results. 

 It does produce genetically homogeneous races. Relative homo- 

 zygosity (95 to 99 per cent) is only approached after from eight 

 to ten generations of the most intense method of inbreeding. 

 The third inbred generation by any method can never give an 

 index of homozygosity of more than 87.5 per cent. Counting 

 a generation every three months, this process of inbreeding would 

 consume over two years. The approach toward homozygosity 

 is very slow. The time element and expense are therefore ob- 

 viously too great for the patience and resources of most 

 investigators. 



THE JODRNAL OF EXPEUI.MENTAI. ZOOLOGY, VOL. 36. NO. 1 



