154 P. L. Krohn 



enough or tliat the ovaries of women have become refractory 

 to stimulation of any sort. 



In tests on rodents, however, Li and Gardner (1950) found 

 that the ovaries of 340-491-day-old mice were just as sus- 

 ceptible to tumour formation as were the ovaries of younger 

 animals. Klein (1952) who extended these observations to a 

 group of old mice whose average age was seven hundred and 

 ninety-nine days, also found that old ovaries may develop 

 tumours, but there was some evidence that they were not as 

 sensitive to the stimulus as are young ovaries. The positive 

 findings in these experiments can be correlated with the 

 continued presence of active ovarian tissue in such old 

 ovaries and serve to distinguish once again the ageing ovary 

 in women from the ovaries of rodents. 



General methodological problems of ovarian 

 transplantation 



Much of the earlier work on ovarian transplantation must 

 face the objection that the experiments were not designed 

 in a way that would avoid the difficulties introduced by the 

 immunity reaction which develops when any tissue is homo- 

 grafted. One way of overcoming this difficulty is to use what 

 may be called delayed autografting. Tissues can be removed 

 from an animal while it is still young, preserved for any 

 required length of time by storage at low temperatures and 

 then regrafted into the original donor. The results of this 

 form of experimental approach will shortly be discussed 

 by Parkes. The method suffers from the inevitable dis- 

 advantage that tomorrow's older tissues can never be trans- 

 ferred to yesterday's younger animals. It is only possible to 

 graft tissues of their more youthful days into animals that 

 have got older. There is also the added disadvantage that 

 the tissue may deteriorate during prolonged storage. 



An alternative approach depends on the fact that some 

 strains of mice are so inbred that tissues can be transferred 

 from one member of the strain to another without stimulating 

 an immunity reaction. Tissues from both parent strains of 



