172 General Discussion 



Cowdry: What kind of physical changes continue in these tissues, 

 Dr. Parkes? 



Parkes: Analyses of the media, in the case of the red cells, suggest 

 that there has been loss of lipids and lipoproteins from the cell. But 

 for details I'm afraid I have to refer you to Dr. Lovelock. 



Cowdry: It seems to me that any biophysical change taking place 

 would almost necessarily be followed by a chemical change. 



Parkes: Well, chemical change must take place very slowly in a 

 medium which is completely frozen up. 



Cowdry: Dr. Krohn, have you any special ideas about the value of the 

 two views concerning ovogenesis? 



Krohn: That is an old subject, which has been reviewed again and 

 again. My personal view is that the organism is endowed with so many 

 ova and does not go on making fresh oocytes. I do not think any of the 

 experiments which purport to demonstrate neogenesis of oocytes by 

 showing mitotic activity in the germinal epithelium of an adult animal 

 are at all convincing. For example, there is another perfectly good 

 explanation for the fact that the mitotic activity in the germinal 

 epithelium is maximal around the time of ovulation. It is at this time 

 that the volume of the ovary and therefore its surface area is greatest. 

 If the germinal epithelium is to act as an epithelium and cover the ovary, 

 it must increase in extent and its component cells will have to divide. 

 Another important point to emphasize is that whenever the total num- 

 ber of oocytes in the ovaries of any species has been counted, the results 

 have always shown that the number decreases as the animals get older. 

 So if there is any neoformation of oocytes at all, it is never sufficient to 

 make up for the losses. I believe that any such replenishment probably 

 does not happen, and that there is this constant wearing away of the 

 ovary's capital endowment of oocytes. 



Cowdry: So according to your view (which I am sympathetic with) the 

 ova in the older woman may be very different from those in the young 

 woman. 



Krohn: Certainly. That is a point, the importance of which I hope I 

 made clear in my paper. 



Parkes: I should like to close the discussion with a figure [see frontis- 

 piece] which is of some interest to gerontologists, the frontispiece from 

 Karl Pearson's essays published under the title The Chances of Death. 



