Discussion 129 



that. We have just started some experiments to see what would 

 happen with replacement therapy, but I think we ourselves have been 

 somewhat misled by waiting too long. If we take a 24-month-old rat, 

 we are surely dealing at that point with an animal in which replacement 

 cannot be too successful since the neurohypophyseal failure seems to 

 start a good deal earlier, possibly at 16 or 18 months. I am really just 

 wondering about the course of the functional decrements in age, i.e. 

 instead of thinking of a sharp fall-off into an old age period, perhaps one 

 should look for an earlier point of inflection in the curve of ageing, which 

 might really be the critical time. 



Miihlbock: What we do believe from our experiments is that there is 

 no point where endocrine activity approaches zero values. What really 

 occurs, in fact, is some imbalance in the hormonal system which develops 

 very gradually. I think that in each case you have to study this im- 

 balance. We have studied the hypophysis, and the dominant function 

 of the anterior hypophysis in old mice was prolactin production. 



Landowne: Do you find that the ability of animals who will accept 

 parabiosis or transplantation changes with age in your material? Are 

 there a certain number of successes and failures, depending for in- 

 stance on whether you transfer a young tissue to an older animal or vice 

 versa? 



Miihlbock: If you use a "take" as a criterion, then there is no difference, 

 but of course there is some relation to time. So, I always say that if you 

 do a transplantation you must have 100 per cent success. 



Landowne: This applies to the old animal as well? 



Miihlbock: Yes, but if you take the development of an ovarian tumour, 

 this will develop in three weeks in a young animal, and maybe you will 

 have to wait six weeks or so before it develops in an older animal. 



Danielli: I am not really convinced that, beyond all question, it is 

 the sense of smell which is involved in these very interesting experi- 

 ments, at least not from the evidence you have presented. It seems to 

 me that it is possible that some other stimulus is involved but which is 

 only operative if the olfactory bulbs are present. And whilst I agree that 

 it is rather improbable that this is so, nevertheless the changes you 

 observed were so large that it would be nice to have absolute proof. 

 Have you any evidence that simply "piping the smell", as it were, 

 of a lot of animals, is sufficient? 



Miihlbock: Yes, we have kept a number of animals in one cage, and 

 when after a week we took them out, took them to another room and 

 put an animal in the cage, the result was just the same. 



Danielli: But then you transferred rather more than simply an 

 olfactory stimulus. 



Miihlbock: Yes, I completely agree. 



Bourliere: A few years ago Le Magnen (1951, C. R. Soc. Biol., Paris, 

 165, 851) carried out some experiments on the olfactory abilities in 

 white rats, which fit in very well with Dr. Miihlbock's experiments. 

 He found not only that rats are able to recognize both sexes on olfactory 

 grounds but that they can also discriminate between a female in heat 

 and one that is not. 



AGEING — III — 5 



