SUSCEPTIBILITY TO TRANSPLANTABLE TUMORS 81 



The trochar method of implantation was employed through- 

 out the experiment. A small piece of the tumor is packed 

 snugly into the base of the neck of the trochar with the blunt 

 pkniger. The assistant holds the mouse firmly with the left 

 hand by the ears and with the right by the tail, by taking 

 hold of the skin of the mouse near the iliac region with the right 

 hand. The instrument is then pushed forward, placing the 

 tissue in the axillar region. The trochar is sterilized in hot 

 water between every inoculation. No ether is necessary for 

 this process. By this method fifty or sixty mice can be inocu- 

 lated in about forty-five minutes. 



c. Go7iadectomy . The term 'gonadectomy' signifies the re- 

 moval of the sex glands of either male or female. Wherever 

 'castration' is used in this paper we mean the removal of the 

 male gonads only. 'Spaying' will be employed for removal of 

 the female gonads. 



Gonadectomy should not consume more than three minutes 

 of actual operating time for the male and not more than four 

 minutes for the female. Ordinary aseptic precautions sufFce. 



Castration. The mouse is etherized until almost all volun- 

 tary action ceases, then placed on the table ventral side up. 

 The assistant holds the mouse by pressing two fingers of the 

 right hand down on the hind legs ; with the left hand it is possible 

 to manipulate a small etherizing bottle periodically and to 

 keep the mouse stretched out by pressing lightly on one of 

 the front legs. The hair on the posteroventral portion of 

 the mouse can be removed by means of straight scissors. With 

 a pair of forceps, the testes are then pushed back out of the 

 scrotum into the body cavity. All instruments used from this 

 point on should be steriHzed in boiling water for several min- 

 utes. A single longitudinal incision about midway between 

 the umbilicus and penis is then made by means of a pair of 

 small curved scissors. This opening need not be more than 

 three-eighths of an inch in length. By pressing the forceps 

 between the outer skin and the body wall, these two layers are 

 separated in the region surrounding the incision. A cut (about 

 three-eighths of an inch in length) is then made through the body 



