128 Discussion 



Miihlbock: We just see that they are healthy and live as long as ordinary 

 mice. 



Best: Have you made the parabiotic union at different phases of 

 inbreeding? 



Miihlbock: Yes. 



Best: And does it always go well after twenty inbreedings? 



Miihlbock: Yes, but it is an absolute requirement that they must be 

 absolutely genetically identical. 



Verzdr: Have you united parabiotically old and young rats, and how 

 was the survival then ? For instance, if you unite a 6-month- and a 24- 

 month-old one, what is the result? 



Miihlbock: They live quite happily together for 3-4 months and die at 

 28-30 months. 



Best: If you did not have this parabiotic test, how would you know 

 if you had a pure strain ? 



Miihlbock: By the transplantability of one organ to another. 



Tunbridge: When you mate a 6-month- to a 24-month-old animal and 

 they die at 28 or 30 months, if there is no cancer what is the spread of 

 amyloid disease in parabiosis ? Is it roughly the same percentage in all 

 organs, young and old, or is it just in the ovary? 



Miihlbock: We have not looked at that in parabiotic animals. In old 

 single animals the distribution of amyloid shows strain differences. 



Friedman: Dr. Miihlbock, with regard to the union of a young animal 

 with an old animal (taking 24 months as the age of the old one), do you 

 have any information about what would happen if you considered the 

 onset of age to occur sooner, for instance at the end of fertility? At 

 24 months you may be trying to reverse something which may be well 

 along and irreversible, whereas actually loss of fertility, if that were 

 taken as the index, would occur a good deal earlier. I wonder if the same 

 idea might not be extended to this question of the transplantation of 

 the ovary. In other words, is there a point of irreversibility if one waits 

 too long before attempting to study the effects of the younger tissues on 

 the older ones? 



Miihlbock: We controlled, of course, the function of the ovaries in 

 the 24-month-old animal before transplantation. We took the ovaries 

 only if there was still an oestrus cycle, which means that they were still 

 functioning. We were, of course, interested in the eternal question: 

 "What grows old first, hypophysis or ovary?" We correlated ovarian 

 function with the oestrus cycle. There is very little margin to do this 

 type of experiment. If the function of the ovaries stops in an animal, 

 say, at the age of 26 months, then there is the possibility that the animal 

 will live for two or three months longer and you can do this type of 

 experiment and can see if the hypophysis is still producing gonadotrophic 

 hormone or not. So far, we can say that the hypophysis produces 

 gonadotrophic hormone. 



Friedman: While it is quite true, I think, that the hypophysis is still 

 functioning, our experiments suggest that there is a fair amount of 

 fall-off in neurohypophyseal function with age; this fall-off, while it is 

 very advanced at 24 months, can be detected a good deal earlier than 



