THE GENETICS OF TUMOR TRANSPLANTATION 297 



1. For routine carrying on of tumors use one or more strains produced 

 and maintained by brother to sister or parent to offspring matings. Use 

 either the strain in which the tumor originated, which should give approxi- 

 mately 100% takes, or if this is impossible, any inbred strain that gives a 

 high proportion of positive animals. 



2. For routine carrying on of tumors at rapid rate of growth, maintain 

 one or more pure strains as above indicated. Use animals from such strains 

 to cross with one or more unrelated inbred strains to produce first generation 

 (Fi) hybrids. Use these for inoculation. They usually grow the tumor 

 more rapidly than the inbred animals themselves. 



3. To use an inoculated tumor as a means of measuring the degree of 

 physiological difference or similarity between strains several steps are neces- 

 sary : Maintain two or more distinct inbred strains, one of which is the strain 

 in which the tumor originated, the other being the strain or strains which are 

 to be compared with it. 



4. The storage of tumor tissue in dry ice refrigerators (about — 7o°C.) 

 has also proven a satisfactory method of preserving this type of tissue. Best 

 results have been obtained when the tissue is frozen slowly, thawed rapidly. 

 Some investigators have found this method satisfactory for all types of 

 tumors, others have reported success with some tumors but unreliable results 

 with others. 



Transplantation or Genetically Controlled Tumors 



IN Relation to the Study of Growth 



AND Individuality 



Factors Influencing Successful Transplantation 



In addition to the genetic constitution as an important factor in deter- 

 mining success or failure of transplanted tissue there are a number of other 

 things which may influence the final result. 



Among these, several may be briefly discussed. 



Diet. — Various experimental, unbalanced and defective diets have been 

 reported as influencing the number of "takes" and the rate of growth of 

 transplanted tumors. There is no doubt that diet may play a part in deter- 

 mining the reaction of the animal. On the other hand, the fact that the 

 investigators have not used inbred strains to reduce and control the genetic 

 variables, leaves it uncertain as to the cause and effect relationship between 

 diet and the changes in percentage of growth. This fact, coupled with an 

 almost complete disregard of criteria of mathematical significance between 



