292 BIOLOGY OF THE LABORATORY MOUSE 



to another host, and, while regularly delaying the progress of leukemic 

 invasion, does not always give lasting resistance." There may be delayed 

 appearance of leukemia or "curious subcutaneous tumors may appear with 

 the histological characteristics of lymphosarcoma." Such tumors have not 

 been obtained elsewhere. When transplanted into normal hosts these 

 peculiar tumors give rise to leukemia of the same type peculiar to the line of 

 leukemic cells previously inoculated. In some cases, however, the inocu- 

 lated lymphosarcoma type of tumor reappears in one or more transplant 

 generations in untreated hosts. This suggests a different type of resistance 

 mechanism on the part of normal tissue to that of leukemic cells. 



The importance of continued studies in this field is thus obvious and 

 should be generally recognized. 



With the general conclusion that the genetics of tissue transplantation 

 has a Mendelian basis, and that the number of genes involved varies in 

 individual cases according to the degree of genetic similarity or difference 

 between donor and host, we may consider certain of the more practical 

 aspects of tumor transplantation. 



Practical Considerations 

 Methods of Transplantation 



The commonest method of transplantation is by use of a trocar. In this 

 and all other types, great care to maintain asceptic conditions should be 

 taken. An infected tumor or site of implantation results in the introduction 

 of factors which importantly influence the continued growth of the implant. 

 A tumor when removed under asceptic conditions and placed in a sterile dish 

 may be cut into a number of small bits. These may be loaded in a trocar one 

 at a time and by a blunt plunger be pushed out through the sharpened end 

 of the trocar after that has been inserted to the site at which the implant is 

 desired. This method can be used for subcutaneous or intraperitoneal 

 implantation. In the case of the former, the trocar can be withdrawn 

 through a constriction formed by grasping the skin with the forefinger and 

 thumb just above the tip of the trocar, thus preventing the implant from 

 being pulled out of place. 



Another method closely allied to the above is the implantation of bits of 

 tissue by fine pointed forceps. This method may at times possess certain 

 advantages of greater accuracy in location of the implant. With the excep- 

 tion of the instrument used, it varies little, however, from the trocar method. 



The use of a fairly coarse hypodermic needle is often helpful. In this 

 case the sterile tumor, after removal, is cut into bits which are then ground 



