THE GENETICS OF TUMOR TRANSPLANTATION 293 



into a mush by mortar and pestle. If an emulsion which will pass through a 

 fine needle is desired the process of grinding must, of course, be more pro- 

 longed and careful. Either normal salt solution or Ringer's solution may be 

 used as a medium for thinning the emulsion. This method is naturally more 

 delicate than either of the foregoing and is valuable in reaching relatively 

 inaccessible or restricted sites. 



Sites of Transpl.\ntation 



The ear. — This provides a site easy of observation. There is a relatively 

 slight blood supply ; however, and the temperature is apt to be below that of 

 the peritoneal cavity or various subcutaneous sites. For this reason the ear 

 is a favorable site for testicular transplants. 



The forehead. — This is a convenient site and one in which the oppor- 

 tunity for invasion of underlying tissue is definitely limited by the proximity 

 of the skull. The blood supply is relatively low. 



Subcutaneous axillary and inguinal. — The paired sites thus provided are 

 very frequently used. The blood supply of both areas is good, that of the 

 axillary region being the better. In using these sites it is well to make the 

 incision through which the trocar or the forceps are inserted at some distance 

 at some lateral location. 



Subcutaneous mid-dorsal and mid-ventral. — These are also frequently 

 used. Accurate location of the implant is more difificult than in either the 

 axillary or inguinal sites, but the blood supply is good. 



Subcutaneous tail. — This region pro\ddes the lowest blood supply and 

 slowest growth of any yet studied. It is advantageous because of ease of 

 observation and because the tail can be wholly or partially removed, thus 

 providing a convenient aid in studies of induced immunity. 



Intracranial. — This site can be approached after removal of a small 

 amount of bone which can later be replaced or through a fine hole drilled in 

 the skull. It can also be utilized by the careful insertion of a small hypo- 

 dermic needle if solutions are used for the implant. Its advantages are those 

 common to the site in other forms. There appears to be in this site an 

 unusual degree of non-specificity. There are several records of successful 

 transplants of mouse tumors in rats, guinea pigs or even pigeons. Quite 

 obviously extensive growth of any implant is accompanied by serious symp- 

 toms and disturbances. 



Intraperitoneal. — Mice are particularly resistant to infection and to 

 operative shock so that any site in the peritoneal cavity is available with 

 comparatively little danger or difficulty. Suspension of tumor cells injected 



